To waterproof clay pottery, first place plastic sheeting or a dropcloth on a flat surface in a well-ventilated area. Use a paintbrush to apply a layer of latex waterproofing compound or waterproofing sealer evenly on the inside of the ceramic pot. Pour any excess latex waterproofing compound or sealer back into its container and wear latex gloves to keep your hands clean and dry.
To achieve a water-resistant finish for ceramic clay, apply either a clear polyurethane varnish or an acrylic floor polish. For example, if you want to waterproof a flowerpot, put tung oil, Thompson’s water seal, or acrylic floor polish on the inside of the pot. Paint and seal the outside.
To waterproof terra-cotta pots for painting or growing plants that need a lot of water, you can do a quick DIY project by placing the saucer or pot on top of styrofoam and tracing an outline using a pen or pencil. The best way to do this is to use plastic cut from a large plastic juice bottle, use sealant to stick the plastic to the pot, then use a pond sealant on the surface.
To waterproof plant pots, place the saucer or pot on top of styrofoam and trace an outline using a pen or pencil. Use plastic cut from a large plastic juice bottle, use sealant to stick the plastic to the pot, then use a pond sealant on the surface.
For small pots, brush the inside of the pot with one cup of white vinegar, two cups for larger pots, then fill the pot with water or bone dry them before coating them with a non-yellowing clear sealer, applying two coats. If not, don’t freeze them.
Using Liquid Rubber is an eco-friendly and cost-effective solution to seal and waterproof all your garden pots, reducing your maintenance watering.
📹 Waterproofing a Planter
In this video I will show you how to Waterproof a Planter. You are going to need an indoor outdoor caulking and some flex seal.
📹 The Best Way To Seal Earthenware Pottery, 4 Methods Compared
Because earthenware pottery is by nature porous, it is important to seal eating, drinking and cooking vessels. Here I try 4 different …
I have waterproofed my light weight rectangular planter 3′ x 9″ with decking oil ( you can give one or two coats) then I just lined it later in the week with heavy polyurethane sheet, (stapled in) followed by placing a few holes in for drainage. The oil has done the job very well, as it has just soaked right through the wood and has prevented rot.
I bought an unglazed earthenware pot about a month ago and filled it with water, and when I came back the following day, water had seeped out of the bottom of the pot and collected in the larger pan holding the pot. I then decided to seal the pot. I soaked the pot entirely in water for 24 hours, and the moment I put it in water I could hear the pot’s porous walls absorbing the water. The next day I came, took up the pot and gently wiped the pot with a cloth, and when the pot was still damp, I spread coconut oil on the inside and outside of the pot. Afterwards, I set the pot in the hot sun so that the oil will fully absorb within the pores of the pot. After the oil had been fully absorbed, I then placed rice water (water wherein rice was left to soak for 1 day) into the pot, along with a little rice flour, and I brought the rice water to a boil. Afterwards, I poured out the hot rice water and allowed the pot to cool off. After cleaning the pot from the residual rice product, I refilled the pot with tap water and placed the pot in a larger pan to see if the pot will continue to seep. After 24 hours, I checked the pot and the larger pan, and, lo and behold, there was no seepage! The earthenware pot was completely sealed and could now be used for cooking.
My immediate thought when you mentioned sealing with oil is to try the Charles Law technique. You heat your oven to 350f. While the oven heats, cover your pot in a food grade oil like linseed or olive oil and let soak a bit. When the oven is heated, place the pottery in the oven for 3 minutes, then remove and allow to return to room temp with the oil still on the surface. The idea is that when the item is heated, the air is pushed out of the pores in the surface. Then when the surface cools, the air is pulled back in, but since there’s a layer of oil on the surface, it gets sucked into the pores. I have done this with a wood cutting board and utensils, but never tried with pottery. The oil will remain in the wood unless it is heated beyond 350 again and has not become rancid in 3 months since applying it to my cutting board. Might be a fun experiment.
I think what most were saying when they said “weight the water” was to suggest you weight out two cups of water (16 oz) with the scale. Then after testing unglazed and glazed pots to weight the water that is left in the pot. That way if you know you started with 16 oz of water and were only able to reclaim 11.5 oz of water you know EXACTLY how much water was lost. Whether the water was absorbed or leaked out or evaporated the pot was only able to “keep” the amount of water you can measure after pouring it out. I know your interest isn’t the science but science methods can provide less intuitive data that is easier to interpret. Just my $.02 Thanks for the article.
Have you tested “blackening” the pot? You pull it out of the fire while it’s still hot and put it in a pot or basket (lined with clay) that is full of a sappy or resin leaves. I prefer pecan, hickory, sweet gum and lastly, oak. The first three will give a glossy finish, oak or grass will give a duller finish. Grass and pine will also cause everything you cook in that pot to taste like grass or pine. Blackening was pretty common in the southeast, especially during the Mississippian era.
Since all your sealers were food products (or food safe in the case of the commercial stuff), I’d have been awful tempted to taste the water out of each one after the measuring step, just to see if that particular sealer made the water taste funny. When it comes down to it, I can’t help thinking a sealer that didn’t make things taste weird would be preferable to one that seals a little more effectively. Love your work, Andy! Keep at it!
This is a very interesting and thorough experiment. Over the years I’ve used a few different techniques to seal some of my clay pots. One of the first pots I ever made I sealed with small leaf soap root. I smashed the root with a stone and smeared the sticky substance all over the interior of the pot. Since then I have cooked in that pot and even used it as a flower vase to hold cut flower stems in water and it has never leaked even a drop. Then I used melted beeswax and that worked excellent as well. More recently I experimented with cooked palo verde beans which are similar to the soap root because of the high mucilage content. The sticky viscous mucilage seals the pores very well. Another method I recently experimented with was soaking the pot in water for about eight hours, letting it fully dry in the sun, then rubbing coconut oil all over the pot and finally filling it with boiling hot rice water and letting it sit for at least eight hours like that. Then I heated up the pot of rice water and then dumped it out and thoroughly cleaned the pot. This method works well too. Pots that are used for cooking will continue to block the passage of water as the fats and minerals in the food clog up the pores of the pottery.
Andy, I use ganosis: beeswax and linseed oil, about 1:1. The wax is melted in oil in a water bath. It turns out something like an ointment. I heat the pot in the oven to 150 Celsius and apply Ganosis several times with a sponge. In my opinion, it is better than starch and milk and does not contradict ancient technologies.
An alternative to weighing the bowls, if water loss is all you’re interested in, is simply to cover the top of the bowls with a plastic wrap, so that any water loss and evaporation take place through the walls of the pot and not the surface. If you were back east, it might not be such an issue, but it our dry desert air, evaporation through the water surface will definitely skew your results.
As a First Nations here in Canada experimenting with this, I always have it in the back of my mind of how my ancestors may have done it. I feel like a cooking pot, for example, after weeks of cooking meals in them would naturally get it’s own sealing from the moose meat, or plants made in the pot. Much like how you season a cast iron. A “good pot” would be one that survives the first few meals and slowly builds up it’s own seal through use. The speed in which the water seeps out would be inconsequential to get past those first few meals. I was also thinking that my ancestors use of starch to seal pots was not like they had a bucket of starch sitting around for this, but again as a few meals were cooked in it the starches from the foods would seal while it was in use. These are just thoughts rattling in my head after reading this and I will definitely make a pot that I can test this.
I don’t know if you need to do this again, since you’ve done a couple. But if you do, you might also include a glass or plastic bowl, so you have a reference for the water it loses do to surface evaporation to compare the others to. Also potentially weighing the water to be more precise than eyeballing. But currently the differences seem large enough that you may not need to be that precise.
Thank you so much Andy! I am looking to seal high fire, cone 10, marbled clay pots. The color of the clay is so beautiful that I don’t want it to be hidden by the glaze but I want it to be safe from oils. This is such a perfect solution. Thank you for all the helpful information you provide. Much appreciated.
Andy, the reason I am interested in exactly how much water is lost to absorption is because I don’t intend to put water in my pottery, but rather food, juice, beer, wine, etc. I want to know which sealing method is going to absorb the least amount of material. Material lost to evaporation is a given and not of concern to me, because liquid evaporates the same regardless of its receptacle. Thank you for making these articles, they truly are awesome!
If you have permission, I would like to give you a recipe. In order to insulate the pots, the Turks spread sheep’s tail oil on the surface of the pot after cooking while the pot is still hot, thus sealing it completely, then it is baked or cooked on the stove for a while to remove the odor. I love perusal your articles, thank you for these beautiful articles you shared.
I would recommend Mahoney’s Walnut oil. it’s a polymerizing oil, it will soak in and polymerize on it’s own; that’s the big problem with mineral oils, they don’t ever really polymerize. (Mahoney’s is foodsafe finish btw; I use it for my wooden lathe-turned bowls) Give it a try if you ever revist this; i’d be curious how it compares..
Thank you. Great article. One thing I would say, that I always advise is never use soap or detergent of any kind to clean no matter how dirty they get. A scouring pad (non impregnated with soap) and water. These pots are porous and will retain the taste of soap making the food yuk, so water and elbow grease only.
I’m sure a bazillion people have already said this but I think this is a really good experiment and it’s a lot more scientific than you give yourself credit for. The only thing I’d change is evaporation. If you do the experiment again you could use a bowl of the same size with two cups of water to compare how much evaporated. You could also cover all the bowls (including the glass or metal bowl) with plastic wrap with a rubber band.
Watching your article reminded me of something. In certain places, animals even fight for access to specific clay wells. It is well-documented that many animals incorporate clay into their diet. Interestingly, the use of clay in human nutrition has a long history and remains somewhat of a puzzle for modern science. I understand that the primary purpose of using a sealant is to prevent food juices from seeping into the clay and becoming rancid. However, this made me wonder if there is any direct nutritional value in consuming food cooked in unglazed clay pottery. Since some clay particles inevitably end up in the food, it seems unavoidable. Lastly, I want to express my sincere appreciation for the insightful and educational article you shared on your website. It was not only entertaining but also incredibly informative. I truly enjoyed perusal it and gained a valuable new insight about the use of clay the made me move on from the kiln oriented process. Thank you.
Thanks so much. Really useful information and delivered in a succinct way with no waffle! (For me you didn’t have to justify yourself over the weighing thing…. like you I just want a sealed bowl at the end of the process),. You definitely explained this very well, with some simple usable methods! 👍
I am really into gardening and I started researching pottery making and I ran into you. I am so grateful. I feel like this is a tremendous resource because the terra-cotta pots are so expensive and have mini gardening friends that want to use the under ground terra-cotta porous containers and I’m wondering if I could experiment with some of these with plants that don’t need as much water is versus the plants that need more water and this is perfect for absorption. I hope to try some of these methods on the parts dispersing more or less water! Thank you very much!
First off I just want to say I appreciate your website. I took a couple of semesters of ceramics-focused art classes in high school years ago but was always leery of the monetary investment in ceramics on my own. Thank you for helping show that you don’t need hundreds or thousands of dollars to start making things. I would also opine that folks commenting on weighing your vessels were likely talking about weighing the empty pots pre-test and then re-weighing after the water was poured out to see how much the ceramic absorbed. Measuring the total volume lost doesn’t differentiate between the angels’ share and the devil’s cut, so to speak. Not sure if this is an experiment you’d care to repeat or if the scale you have at hand can measure in small enough increments to tell the difference, but I offer my thoughts. Thanks again!
This is most certainly science. It may not be the most accurate science with several variables that weren’t tightly controlled, but… You came in with something to prove, proved it, and most importantly, documented it. This is science. Someone can now take this and replicate it because it has been documented.
I willing to bet that they used a bucket of milk to submerge the clayware (i.e., a bucket of milk was fresh milk, sitting, and they just submerged the pottery, then used that milk later for cheese, etc) and the starch? They cooked a big pot of starch, then submerged the pots, then kept it cooking the remaining starch for glues, or even to thicken other foods, maybe candy. My overall impression is that nothing would be wasted from anything in the past….much different than how we live today. Its sad, but I am glad you are explaining these principles to us today. Thank you!
Thank you so much for your articles! I am learning so much, and I love your style. I have a question. After you seal your pottery, do you need to seal it again in the future? I am thinking like how after you use cast iron you need to re-season it every time. Does pottery need re-sealed after it is used for food?
Heh, I think that the responses to this kind of article really show the wide appeal of this website. Some people are artists, some are interested in the history or re-creation of it, and some (like me) are more interested in the technical aspects of pottery. So it’s understandable and tempting for me to go “ooh, try this… ooh, measure that!”, or even to correct how the comparison happens, but that’s not always the most helpful thing to do. Shoot, for me personally, I LOVE hobbies that require measuring precisely, like espresso or homebrewing or baking… but that’s not necessarily fun for everyone else So in short, thanks for the comparison, and also it’s fine to set boundaries concerning your methodologies. Shoot, I kind of want to try out some sealing methods myself!
As a few alternatives depending on what you want to call native or local, coconut oil is great to work with as it warms easily but can take a fair amount of heat, but even with a light braze of 600*F it will taste nice afterwards. Food grade carnauba wax is often found in a lot of bamboo wax conditioners and I’ve used that on a lot of cutting boards. In conjunction with the coconut oil on coffee cups and repeat heat cycles, I could see that being rather nice. The third and perhaps most universal for historical purposes, roasting coffee beans releases an absolute jewel of an oil that penetrates metal (all my roasting pans for coffee beans take on a golden brown hue) and I may try lining a once-fired piece in green coffee beans to see how that goes. Wouldn’t that be a honey of a selling point for an earthen coffee cup! Add: Ah, almost forgot. Casein from milk was used historically for bioplastic production in conjunction with another material which escapes me at the moment, but possibly a guar gum. Might be worth a read. Casein can be found in powdered form as it comes back and forth into the sustainable products fashion every few years.
Hmm. Those medium-sized bowl-shaped pots on the thumbnail, and the ones you fire on the article, look like they’d make PERFECT vessels for biggish handcrafted scented candles, the kind with several wicks! I honestly don’t know if they would need sealing for that. Have you thought of selling to/doing a collaboration article with that kind of crafter? 🙂
Another method of milk soaking, is one I saw where after the oil lamp, in this case, was fresh out of the fire and still hot, he submerged it entirely into a big bowl of milk, and let it cool off there. I have not tested this at all, but with nothing but my intuition to guide me, seems like you could achieve better results maybe? I have not tested it at all, but at least I imagine you wouldn’t get that line of milk residue where the surface was, and it’d get evenly coated.
This is great science! Just a thought for your NEXT sealant article (do several, we obviously like them and you’re doing great): Make each bowl > apply the sealant to each bowl > note the weight of each bowl dry > add the weight of one cup of water (240g) to each bowl (place dried bowl on scale, tare scale, add 240g of water) > note the weight of each bowl with 240g of water > let all the bowls sit for X period of hours/days > place a new/different glass container on the scale and tare the scale to zero it out > pour one bowls water into the container noting the weight of the container in grams > weigh that same emptied bowl, noting it’s weight in grams > clean/dry out the glass container > continue this process with each bowl until the experiment is complete. This will provide you with the following: Beginning results: 1. The weight of each bowl 2. Constant = 240g of water Ending results: 3. Precise water that was held/emptied from each bowl (the added weight in the container with each bowl’s respective water) 4. Precise water retention/absorption from each bowl (“emptied bowl weight” minus “dry bowl weight”) 5. Precise evaporation from each bowl. (240g – (#3 + #4) = The evaporation coefficient Isn’t science the coolest!? This isn’t much more work than what you are currently doing, just more accurate. 😉 If you have time and looking for more content for your website, please humor us with the above experiment by trying the same or different sealing products/methods. I love learning, keep up the good work.
I wonder if there would be any difference between the milk used here, and raw milk. Also, walnut oil is a drying oil, has a high smoke point, and is often used in cooking so it can be found in many grocery stores. Flaxseed is the same plant as linseed, and you can find flaxseed oil for cooking as well, although it does not have a high smoke point, so not for use in high temperature cooking. Just in case you wanted to try a food grade polymerizing oil, you’ll probably have more luck looking for those.
Hi Andy, and thank you for your articles, i learned a lot on your website ! I’ve a question and you’re the only one who can answer it : I want to craft some earthenware pottery, and i’m currently building my own kiln ( more like a Galo-roman wood fired kiln : for the historical accuracy of the French city where i live and for having a better control of the temperatures ). I would like to make some bonsaï pots ( my main hobby ) and other objects related to agriculture. As the weather is kinda freezy in winter ( -10° celsius sometimes ), i would like to know if the earthenware homemade pots won’t break when i water the trees during cold days ? The clay i use comes from a river, it’s really pure, really plastic and kinda red/brown. As you adviced, i mix it with temper, wich is fine sand. Hope you’ll find my message, and thank you in advance if you take the time to answer it.
How much would a unsealed pot the same as them loose in the same amount of time? Using a ‘control’ unsealed one would have shown how effective they are. Great article tho I like how you are old-school doing it like the ancients 👍 maybe the one that lost the most but had less absorbed was because it pretty much went straight through to make the puddle but the others the water found it more difficult to get through as they were more effective??
Be aware, if you try linseed oil (you can get it at health food stores as others have said) food grade does not have drying agents, so it takes 2-3 days between coats (since it’s not technically “drying”), at a minimum to let it set. And it could be a couple months to fully polymerize, depending on how thickly you apply it. But as long as the surface is solid, it should be useable, even if the core is not fully cured.
One of the techniques I’ve read about was putting dried corn cobs in the pot, then sealing the pot and sticking in a bed of coals. The pot gets very hot, and the cobs start to scorch and smoke, but so long as no air gets in, the oils won’t ignite. The resulting smoke seals the pot. Another issue was adding physical designs to the pot, such as checkered and lined patterns. It wasn’t just to make them beautiful, they also increased the strength by interrupting potential shear lines.
You mentioned that linseed oil might make a good sealer because it polymerizes at room temperature (but didn’t try it because you couldn’t find any food-grade linseed oil). Painters who work with oil paints know that egg yolk will also polymerize at room temperature, and was commonly used until they switched to using linseed oil-based paints. It might be an interesting experiment to see if egg yolk could be used to seal earthenware pots.
Hey Andy! I have an idea! And it could be a long lost ancient technique!! What about fermenting in the pot? Add fruit, sugar, water and yeast to the pot. Cover with cloth to keep bugs out. Maybe cloth and a board to let less air in. Let it ferment for a couple weeks, then bake it (drink your prison wine if you dare). Yeasts create their own fine sediment and would probably live in the pores of the clay. Could clog things up. Might be a fun experiment. Also, why not use pure corn starch or potato starch? I know the idea is primitive, but you’ve used other processed materials
Hi Andy, I have been inspired by your website so I went down to the river and harvested some red clay here in Tennessee. I’ve allowed it to dry and I’m hoping to dry process the clay however I can’t seem to find a corn grinder like you have in my price range. Will a manual crank meat grinder do the job? Thanks so much for all the information you share!
Hi! The weighting is to know how much liquid absorb, just for curiosity, I suppose. We are not making science, we are trying to recreate something OLD and useful. I would try submerging them in the substances so has a better opportunity to even distribution. Thank you for all your experimenting and for share them with us.
I watched a traditional pottery documentary once where they used milk to seal pottery, but the way they done it was to take the hot pottery after they had finished fireing and extinguised the flame by putting a bunch of leaves and soil on it, which left the pots with a black finish, then they took a little milk and poured it in the hot pottery and swirled it around inside the pot. It looked like it worked really well and didnt leave any residue, but maybe they just didn’t show that. To avoid thermal shock perhaps they heated the milk first im not sure, they used the same maybe a cup or so of milk to seal many large pots.
This was a great article. I am gonna contradict you on one thing though; it definitely was science. As others have said, heating the lard isn’t quite sufficient to polymerize it. I would recommend heating it to about 400F for a couple hours, then turning off the oven and letting it cool completely with the door closed. You’re basically trying to reproduce the same coating as cast iron, and it takes a while. On the plus side, if you do this a couple of times your pots will be waterproof, and any loss will be attributable to evaporation.The polymerization is basically a “natural plastic”. As I’m sure you know Indian cuisine uses unglazed pots seasoned this way. Also, have you thought about combining beeswax and an oil with a high smoke point then baking it? I’m curious if that would be better or worse than the Howard’s alone.
The reason people are wanting you to weigh the bowls is that it gives you a more accurate indication of how much water was lost. Some water sticks to the bowl, and therefore isn’t accounted for when you measure purely by volume. In this case, it’s probably needless precision. It’s not like you’re testing the claims of a commercial products to see if they’re telling the truth. This is simply, “Of methods A, B, C, and D, this worked best for me.” If those people want high-precision measurements like they’re discussing, they’re perfectly welcome to do the test themselves, and make their own article about it if they so desire. I can think of a couple things I would have done differently in this test, but if I want that information so badly, then I can do my own tests, too! It seems like some people are thinking of you as if you are some paid instructor, who needs to spoon-feed them every bit of information. You’re not. You are giving people a starting point and helpful advice. There is absolutely nothing stopping your viewers from trying out ideas on their own. If someone wants to know if they can mix horse pucky into the clay to achieve some specific goal, then they should try it! One of the best ways to learn is by doing. perusal articles can give you a starting point, but people really need to try it out for themselves.
Thank you Andy. The weight results helped me to see that Milk sealing beat out all the competition. The volume loss of Milk was similar to the results from the Howard’s, yet Howard’s appears to have allowed a greater amount of water to pass through the bowl. Milk sealing seems to have given the bowl a greater ability to retain water within the sealed bowl, meaning the water was still retained despite being locked into the structure of the bowl.
i just made a candle holder! it looks like a little mug, it has a rim to catch the wax, and i actually used a candle stick to make sure it fit! and i think im gonna seal it WITH wax (ironic enough) though, it shouldn’t need sealed, but cosidering how i go by: everything is multi purpose if you use it for multiple purposes, i might at some point end up putting water in it! and i made the little handle using my finger as a template, of course i gave it some good wiggle room, and it’s just basic, and flat based! and for my first real pottery (besides the sexy lady i made i baked in the oven, but that was before i figured out how high the temperature needs to be) and im gonna fix it up after it dries (cause it’ll crack a little when it dries) and because it’s dry, it’ll also give me a better, harder base to build onto, of course i still gotta wet the base so it’ll stick but y’know! OH! and i did it with JUST my hands! well, and a knife, but besides that all i needed was a cutting board, my hands, and a red solo cup full of water! my hands got all gross and dry, even after i washed my hands, so i just used lotion. that fixed my hands. and i had like 4-6 buddies helping me… the ants! they were helping, i don’t know how but they totally were… actually i think they were just collecting some of the clay for their nest, but i didn’t mind, i had plenty to share… well i barely had/have any at all, but i didn’t need a lot anyways!
Ok so today I was at my local Asian mega super grocery store and I found a clay pot that I wanted, knowing nothing about it. I wanted to making crusty clay pot rice. Now I’m down the clay, clay pot rabbit hole. I loved this article, and I’m so glad I found it. I never thought of pottery as anything else except for decoration. A whole new world. I cook a lot with cast iron and I use the cast iron bees wax/oil mixture to season them regularly. I think I’ll be trying some of that after I soak the pot a bit. The historical context of this information is also super fascinating.
If I had to find a justification for weighing the pots, its that if the water isnt there for the volume measurement, but is for the weight, its not leaking through so you only “lose” water once, but if the water isnt in either, Its completely lost and youll keep losing it, It could be that an interior coat being in direct contact with water is less effective for some methods than others, so youll get a lot more “soaking” on those, but they hold up better out of direct contact and form a better seal that way, or one of the sealants is just more willing to adsorb water. Its a bit hard to tell these sorts of things from just a volume measurement, but a volume and weight can give an indication one way or the other if any of the above are happening, not necessarily what one though. bowls designed to hold water for any length of time are likely to be in use near constantly, so it simply soaking the water up but not letting it seep through, versus one that loses less the first time, but lets it seep through is likely to be a significant factor for water loss. (1oz now 10oz over a week vs 8oz now 2oz over a week sort of thing)
If you do this again, it would be interesting to do a control in the experiment. Use a glass or plastic bowl with the same surface water area. You would be able to find out how much of the water evaporated as opposed to leaking through the earthenware. You just subtract the evaporated amount in the control from each test bowl and find out exactly how much water leaked out of the earthenware. I love your website by the way.
As others have said, this is science in the broadest sense, even if you lack a white coat. That said, it would be nice to have a control bowl (untreated) and perhaps a glass bowl of similar dimensions (to see how much is lost to evaporation, so that the results can be better extrapolated to lidded pots).
If you were using an earthenware pot to cook cornmeal mush in, it would gradually acquire a good layer of starch to seal its interior surface. And cornmeal mush is a nutritious foundation for a meal – float a fried or poached egg on top, or some kind of cooked meat, or else some berries or maple sugar.
I get it. Science is fun. What isn’t fun is when folks invalidate the project by saying it wasn’t properly done scientifically. Who wouldn’t dislike that? Scientists like artists need to remember to be constructive when discussing experiments and not get all pedantic about the scientific method. We as creatives (scientists and artists) need to be more gentle with each other and more supportive of the goals of experimentation, discovery, creativity and science. They are compatible and most experiments are useful. The results can be refined-yes but with courtesy and respect for the process. After giving proper respect (goes both ways) then a suggestion for refinement can be given. That is my rant. Thank you:)
If you did want to weigh them, you would way the bowl after filling it with water and again before pouring the water out. Then the difference between the weights would be the amount of water that was evaporated, leaked out, or consumed by wall gnomes. It would be a useful measurement if you were planning on sticking the bowl in your mouth and sucking out all the moisture trapped in the walls after each use, as the way you measured it only included the useable portion of the liquid.
Andy, hello, College Ancient greek pottery temps around 950 c, Ancient greek pottery can be so fine it looks and feels like a paste, then kiln fired under a late carbon reduction cycle, pottery comes from the kiln, and is porous,A clue to making the pots less porous comes with the decoration paints defined as Terrasigillata . a colloidal sus(ension of the pot clays left to sit for 12 weeks or more, the clays separate leaving one with a thick red gloss paste . applies after making by many thing clays the clay once fired is less porous . The Romans made a Semmian ware bright red using this method. you can test this via some spit on the pot, you may need to fire higher,
The weighing kind of indicated that the more moisture the bowl holds, the better it is at container the water. The worse the bowl is at container the water, the more water will seep out, meaning when you weigh the bowl it’ll be lighter than a bowl that is better at holding water, since it keeps the water in.
Weighing is just a way to differenciate between soaked in liquid and evaporated liquid. Will show more precise data and also give a better idea of how well the sealers work. You would weight prior, do the test, then weigh after and also measure the liquid. With this data, you could find out where any water went.
There’s yet another oil that could potentially work as a sealant due to its ability to cure into a food-safe varnish: walnut oil. Walnut oil also has those unsaturated oils that cross-link when they oxidize, similar to flax seed oil. If you use walnut oil, be sure to get stuff that doesn’t have added antioxidants, such as vitamin E / tocopherol, since it is precisely the oxidation that kick-starts the cross-linking that causes it to cure into a varnish. In a pinch, you can make your own by blending walnuts in a blender until you have walnut butter, then straining the walnut butter or just letting it sit until it separates into solids and extracted oil.
cool !! what about evaporation ? specifically if the atmosphere was dry during part of those 13 hours… evaporation may take out some (how much ? negligible ?) of the water even if no water was seeping through the pores of the vessels… sorry, i’m not suggesting that your next experiment could include a standard glass vessel for comparison, or use lids for the earthenware 🙂 this non-science science would never end 🙂
Weighing the bowls makes sense if you use the metric system: 1 millilitre of water weighs 1 gram, so you could accurately measure how much water has soaked into the ceramic. Measuring the change in volume of water measures all losses (evaporation, retention in the ceramic, and flow through the ceramic). I hope that helps.
The reason people are worried about weight is to figure out how much escaped out the top, because that amount is going to be the same out of all of them, just to eliminate a variable. Issue is they’re not taking into account that liquid is seeping through the walls and evaporating that way so weight isn’t gonna tell you anything volume doesn’t. I feel like the best way to test it would be to put a plate over the top of all the bowls, then doing a volume measurement like you’re already doing, if only to figure out exactly how much is being lost through the sides. I can see why people would think weight is a good test, but it’s only a good idea in a world where earthenware never has lids, and doesn’t evaporate out the sides like an Ouya. The test you’re doing is fine though because most people don’t put lids on bowls anyways, and this is a test of function / utility, not a lab experiment.
The simple answer to the weighting question, it is more accurate because you remove the human factor in measuring. That’s why when you cook, it is best to use weight to measure ingredients rather than cup measurements. Also, you should have weighted the water you were putting in and taking out, not the bowl this would tell you how much water loss you had but, saying that measuring the bowls did teach us something. For example, the lard seal lost a lot of water and did not gain much weight, which would indicate that it is the worst as it does not seem to stop the water going through the pot. You should try peanut or some other vegetable oil of some type heated in the oven, like used to seal woks. I’m not a 100%, sure, but I believe when oil is heated it turns into a type of POLMAR. It appears to be safe as it’s been used for a long time and I have not seen any research to say otherwise.
I am late to the party, but as a chemist, I do have a suggestion – a liquid glass could work as a sealant. It is a water solution of sodium silicate and here in CZ it can be readily bought. As per google, it should be available in the USA too. When something porous is coated with this solution, it reacts with the carbon dioxide in the air and forms sodium carbonate crystals on the outside, leaving insoluble silica behind. It is used as a binder for fireclay and as an accelerant and sealant for cement (it makes the cement to harden faster and to be more waterproof and less porous after it hardens). It can also be used to conserve eggs for longer time because it seals the pores in the shell and thus prevents them from spoiling.
Weighing just adds greater depth to your understanding of what’s going on. In the case of lard it told how differently it was working compared to the others. If you start with the assumption that all of them lost about the same amount of water due to evaporation, and then see that it lost the most yet retained the least amount of water in the clay, that tells us it isn’t just retaining the moisture in the body of the bowl like the others, but is letting more liquid completely pass through. the others slowed both the water’s rate of absorption and the rate at which it released it on the other side. we can also extrapolate more easily from those little nuggets that as surface area and volume of water increase, it will most likely show an even more drastic decrease in effectiveness compared to the other methods. So, in smaller wares it won’t matter much, but in larger vessels that need to be sealed, prioritizing other methods than lard will give you a better result. Or it tells us that if, for whatever reason, you need a large vessel that holds water better than unglazed pottery, but still needs a certain degree of porousness for whatever use you’re putting it to, then lard should be your first choice.
Soaking the bowl into the hot sealing product would penetrate deeper than simply brushing it at a room temperature. I”d prefer pure bee wax or bee wax combined with linseed oil rather than a petroleum product such as this conditioner. However you purify it, there’s always yucky aromatic compounds in petroleum based products. By the way, I am pretty sure bee wax is a more ‘ancient” pottery seal than conditioner, I would have tested bee wax before anything else, before even milk, as milk proteins or fat probably degrade fast into more toxic compounds, especially if you store liquids other than water. Bee wax has some propolis in it that has antibacterial properties or something. Linseed oil mixes very well with clay: People are actually using it on top of clay floors, as the oil makes a pretty good seal after it oxidizes, and does not mind the occasional splash of water, unlike untreated clay floors. Maybe include a comparison with a glazed bowl too, to get a proper reference for the loss by evaporation only if you don’t use lids treated with the same sealing product. Good luck with your workshop!
Walnut oil is another traditional polymerizing wood finish. I like to warm it in the sun or microwave to help it penetrate deep. One warning that should always be added to polymerizing oil use is that they create heat when they cure. Rags or brushes you use with them should be washed with soap. Oily rags in the trash can self combust.
Food grade linseed oil is literally just flax seed oil. Should be available in the organic food aisle of any grocery store. “Boiled linseed oil” from the hardware store has been treated with harsh chemicals and drying agents that help it cure and prevent it from going rancid. I’ve been boiling my own 17th century surface sealer for woodworking for years with great success. It’s just equal parts of flaxseed oil, beeswax and turpentine (also works well with tongue oil instead of flaxseed oil). Sometimes I will add in 5 percent pine pitch, pine tar, or pine resin, or I will add in 5 percent chalk, charcoal, slaked lime, talcum, gypsum, clay or iron oxide. When properly burnished it completely fills the porous surface of the wood and gives it a beautiful and durable surface that is semi glossy, 100 percent waterproof and UV stable.
If linseed oil is not available use a walnut. Walnut oil is a very fast drying oil and instead of buying a store bought pressed out walnut oil that has a very limited shelf life just go natural. Take a walnut kernel press on it with anything to break it up a bit and smear it on whatever you want to oil. A bowl might require 2 walnuts to do the job but it is not hard at all.
I am trying to seal unglazed clay diyas (small lamps used in India for ceremonial purposes). Oil is poured into the diya, a cotton wick is placed so it hangs out 1/8 inch or so from a spout in the rim of the diya. Then you light the wick. Over time, with daily use, oil soaks onto the diya. Is there a way to seal these so the oil does not soak through? Thank you for any help!
Would a starch-sealed olla still work for cooling the water? I find that unglazed pottery leaks a bit too quick, but I’m afraid that a starch-sealed olla might leak too slow to get that cooling function. What are your thoughts on this? If you haven’t tried, it would be interesting to see a comparison experiment on this.
Comparing the weight before and after the 13 hours doesn’t account for how much water is held within the clay pores when you measure so comparing the volume of water as you did is more helpful. All you have to do to make this science though is to write down your hypothesis that adding more layers of sealant will improve performance, then experiment and document the results. Also if it’s not science it’s still engineering!
One tip for “seasoning” the clay with lard: don’t put a huge amount on the pottery. In your article, you applied far too much lard for a proper seasoning style sealing, if my knowledge of cast iron and carbon steel cookware is applicable. Apply the barest amount, then wipe it off so thoroughly that it’s as if you didn’t want it it on there in the first place. Wipe it off while the pot is warm so the lard is liquid. The heating/smoking process works best when there is hardly any oil there at all. In fact, I’d warm the pot up for 10 minutes at 300˚ and then do one more wipe down to get any lard that has liquified and come out of the pores. Then, heat that barest amount of lard up to the smoke point. Repeat this a couple times, and the pot should be properly seasoned. If you apply more than the barest amount of lard, it actually doesn’t work as well, because the first coat is supposed to bond to the material you’re seasoning, and not to other molecules of lard, where you end up with a gummy rancid coating. The second coat is supposed to bond to the solidified residue of the first, rather than to other molecules of lard, etc. Eventually all the pores will be closed up, but each coat will have bonded to the solidified prior coat.
You should use evaporated milk, not fresh milk. When using fat to seal, like with cast iron, one should put on a little and then wipe it off like you made a mistake putting it on in the first place, then polymerize it in the oven. As to science, the difference between science and messing about is writing it down. What you’re doing is indeed science. Just home science.
I think you’d get a better result if instead of regular lard you used rendered kidney fat i.e. suet. It has a higher melting point than lard and is harder and waxier at room temperature. Also contrary to your assertion this article is in fact scientific; you don’t need to test a hypothesis. You carried out an experiment, you documented your methods, and you published your results. That’s tangible science right there.
Unnecessary measuring is unnecessary. What is “science”? if not a certain clarity in the aims of the investigation, of its process and of the results. In this sense your test can actually be labelled “science”, whereas many “scientific” papers cannot. The Greek founders of science like Archimedes often did not have a very elaborate machinery to help them but relied on quite simple methods, even to measure the circonference of the earth. If weight should be used, perhaps it would make sense to weigh the water poured inside the vessels and then weigh it after just to have a more precise number on the volume, but you have so few parameters to compare here that this may also be unnecessary as the results answer the questions.