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There is no inner mold with the plaster shown here for the body. The slip is poured in and back out. And you can have inner molds with slip casting as well to make solid cast parts and/or double walled parts.

Yep, I've seen it. While they look similar at a high level, a lot of the specifics are different because of the different materials.

Great! Yes, the best way to know is to test.

This is done on a 3d printer

This is old forge creations' first five floating recipe and a purple mason stain. Here's the base recipe: glazy.org/recipes/144590

These molds are intended to be reusable several times so the frozen trick allows that.

@PotterybyKent understood! I guess windscreen washer fluid might be a pretty good premade easy to get solution for the ice bath? Cheers!

It might. Basically you want a solution that stays liquid at freezer temperatures so you can pour it in and out, and get it as cold as possible without needing special equipment.

You're welcome!

Cone 6

I would imagine so, but I don't really use many commercial glazes. You can start with just your regular transparent glaze and see how it works for you. Also, if anyone else here in the comments has any suggestions, feel free to add them.

Thanks!

In that case the clay will be shrinking around the plaster while in the mold. As such, I think the handle design needs to accommodate that. And the 3d printing is indeed easy - the more involved part is the 3d modeling.

You're welcome!

The key really is to make sure everything is mixed up well. So depending on your method of mixing and volume to mix it might take some more time, but there shouldn't be any different in the final results. I've seen lots of people use a drill attachment in a large bucket (similar to how I mix my slip) and that seems to work just fine.

It seems rather unintuitive for many!

No, I don't treat mine in any way. In general the molds are meant to be consumable - they will wear out over time. So I just make new ones as needed (pour plaster in the 3d print again). The hardness of the plaster comes down to the plaster type. For slip casting a softer plaster is actually beneficial. It's not so much about being soft as it is about having a high porosity (lots of tiny holes) to absorb the water. Some people make their molds out of different plaster which is stringer, but the tradeoff is the mold is much much slower. I'm not exactly sure what might cause a difference between different sides of the same mold without knowing more about how it was made.

@@PotterybyKent thank you for your answer and sorry for mistyping your name :) I made my molds in the old fashioned way, I put my master in a small bucket upside down and then I poured the plaster all the way up. As a result what is the top in the bucket is my mold's bottom and since it haven't been treated with any oil or wax it always becomes a bit different comparing to the sides which had contact with bucket and its oiled sides. I do not treat the final mold but I always oil my buckets sides with coconut oil (:D) what makes easy to separate plaster from the bucket - as a result all sides become very nicely treated apart cthe bottom. I always wondered what proffesionals do and how they treat their molds since this is my way and not sure if it makes sense. Thanks!

I pour mine the same way - upside down - so that the bubbles rise from the surface. One guess is that your oil is interacting with the plaster in some way (do you wash it out after the plaster is cured?). It might also be the way your mixing the plaster so that the top is more fragile. But those are both really just guesses. Some people will refine the plaster once it is mostly set (eg smooth it out with a rasp, knife or the like). That could deal with any unevenness on that face of the mold. If there are sharp corners - those are often more prone to breaking so rounding everything off can help.

@@PotterybyKent Thanks Kent. I think you are right. Sometimes when I do make them I see that after the plaster starts to get thicker it pushes all the water to the top of the bucket. The plaster becomes strong but there are still some water on the top. Thats how I know that I probably failed with my proportions so I just pour the water from the top away and leave it to dry. That might be the reason too. From the other hand, I am starting to think that maybe there is nothing wrong with a bottom - just the sides became super strong after interacting with oil :D and thats why the bottom feels so fragile in comparison. I wash my molds after I make them but just with a sponge and quickly, feels that oil is well absorbed by the plaster and I can't wash it away much :) Thanks a lot from your insights, very helpful and interesting to discuss about these topics with someone :)

Ah, the plaster definitely should not separate like that when wet. That is why it is weaker and would be the root cause of your issue (and that is unrelated to the oil).

Thanks!

It's all about orientation. You want the blade to be parallel to the slip well shelf. You need to go down at an angle to get started but then quickly flatten out. Also I hold the blade pretty gently and there's not a lot of force. The clay is still super soft at this stage (way softer than the paster) so I just go nice and easy and feel for the plaster as I cut. (This also is using the fact that the Shape Cast slip wells are nice and flat so that makes it easier as well).

@PotterybyKent Thanks, I'll give it a try!

Good luck!

Starting bone dry means you know the water levels, which is a huge variable you can then control. There might need to be some extermination for your particular slip, but it is worth trying for sure! And in the worst case, let it dry out and try again.

Cheers!

Sorry I missed that one in the description - let me add it. Yes I do. It is this one here: amzn.to/3C7ZonL

I actually have one just today! This focuses on reclaim, but it is very similar for dry slip as well. I do have some older videos on making slip as well. For beginners, I recommend buying premixed slip - it's just one less thing to worry about.

@@PotterybyKent awesome thanks

You're welcome!

That's awesome! Lots of new toys to learn and play with!

That's great to hear!

That's great to hear!

It is liquid clay called slip.

@@PotterybyKent Thank you very much for replying me 🙏🙏🙏🙏🙏 Is it one chemical or do you mix different chemicals? I have made a plaster mold, I make things by filling the mold with plaster As you know plaster is very heavy, your method is great, it just creates a hollow body. I am from Pakistan I want to learn your method 🥹🥹🥹

Slip is made from clay, water and a chemical deflocculant. This process is a common way to make ceramics.

Thanks! In shape cast directly, no not yet. However this is pretty easy to do with the leather hard clay. Either carving or applying more slip. It's been awhile since I've done this but I do have older videos showing some of those techniques.

Thanks for following this journey!

I found a way to seal everything so the plaster doesn't leak, and can then be released. Check out the play list to see how it all developed and what I do now.

Thanks! I want to understand - if you're making the inner mold thicker, then what is the purpose of removing the need for supports (you're using the material and time either way). Also, I'd worry about making the part more rigid as it needs to give a bit during removal. For the screw holes, they're very small and print without supports (or if the slicer insists, you can turn them off for right there without issue).

@@PotterybyKent The two places that would be thicker would be the slip well, and the new inner ark at the top. The draft angle at the slip well could be slightly increased to offset any increased resistance to release, you could also pull against it with more force without breaking the bottom ring where the thread insets are at. I can see where adding the ark at the top could be more problematic depending on the outside shape and its draft angles. If the supports required can be minimized it would also decrease the overall print time. None of this should be taken as criticism to the excellent work you are doing. I'm just starting to play with pottery and you have come up with an excellent method of cheaply and quickly creating slip cast molds.

I got it. I could see redesigning the slip well (although since it is so close to the build plate there really isn't much support there). And it's not so much about force being applied (you shouldn't need much) as it being able to deform just a bit (shrinking w/ the frozen mixture).

Thanks, glad you liked it!

After doing all of these experiments, and having time to reflect, I think the actual solution is to go a different direction. I think I need to change up my clay body so that it is more plastic.

TPFE would be best. But for the number of holes I had, it was too much $ to justify.

@@PotterybyKent You're right that teflon rods would be good, but they're much too expensive. Something ultra-cheap that might work would be plastic straws cut to an appropriate length. I suspect these are made from either PE or PP (most cheap disposable products are), but you'd need to test to see if the slip would drain from the plastic as well as it does from wax. The obvious problem with a straw is that it is hollow, but you could fix that by filling it with another substance before cutting it into pieces. Many things might be suitable, but silicone caulk or perhaps expanding polyurethane foam (supplied in aerosol cans and used for filling cracks) would do the job. In fact, a plastic straw might function as a very good mould to make rods of pure silicone! Fill one with caulk and then carefully score the straw lengthwise, and you have a silicone rod that probably won't stick to anything.

@@PotterybyKent Another thought would be that if you use a straw to create silicone rods, but the result is too flexible, you could likely fix that by putting a steel core at the centre of the straw before filling it with silicone. Straight sections of steel taken from a cheap metal coat-hanger would be suitable for this, and if the steel isn't perfectly centred, it wouldn't really matter as long as it is fully coated. Numerous other metal objects (brass rod, etc.) could also be used for this, though it would be needlessly expensive unless you already have some on-hand.

Metal didn't work as I thought it might

@@PotterybyKent No, I agree that metal alone likely wouldn't work, but if it is surrounded by a layer of cured silicone, the results would probably be good. A steel coat-hanger has a diameter of about 1/16th of an inch, and the internal diameter of a typical straw is at least twice that (1/8 - 1/4"). Using a plastic straw as a mould, with a central core of steel (coat-hanger), and surrounded by silicone, should give you a reasonably rigid but clay-repellent rod that could be cut into pieces to provide what you need. You'd need to check that the silicone doesn't bond too tightly to the plastic straw, but if it does that problem could likely be fixed by coating the interior with Vaseline or talcum powder.

If you do try, let me know! The spray paint actually stays on the mold, so even when reused, it doesn't need to be reapplied. (And if you're glazing your pots, you likely don't even need to smooth out the print. Between, a bit of sponging, clay shrinkage and the glaze, layer lines disappear in practice.

Yep, I'm worried about the 3d print deforming under vacuum. For other kinds of pours, pressure is often used and I've heard of similar concerns there (but it's probably worth testing).

Interesting ideas. For several of these I have videos on why they won't work or I'm going a different way. Eg the ring is separate not only to aid in demolding (which is needed - one could CA glue it in place), but also due to print bed size limitations (the molds get big fast! due to clay shrinkage and space for the plaster). I actually have a solution for removing the inner mold that involves freezing. But you don't want to freeze the still curing plaster as the expanding water would likely mess with the paster porosity.

I have not (they weren't an option when I started Shape Cast development). However I'm guessing they would work ok, at least the first time the mold was used. I'd be curious how well they grab once it is disassembled and reassembled. If anyone tries, do let me know!

Correct - it isn't the alcohol specifically - you want the mixture to be liquid at freezer temperatures (which is a fair bit below the freezing point of water). That lets the 3d print shrink just enough to overcome the growth in the plaster and vacuum formed. Right now, Shape Cast does not support that. It is something I'm thinking about. However most features on the surface of the pot would require a multipart mold. It is also possible I could do a custom design for you.

These were fired in my glaze firing which is cone 6 (and matches my clay body).

It is casting slip from my local pottery supplier. I recommend you reach out to your local supplier.

As you found, this type of geometry is indeed hard to do with slip casting and is likely dependent on the details of the form. I have seen successful double walled bowls and mugs which have an inner plaster part in a similar way. I think part of this is also size dependent (something smaller will shrink less in terms of absolute size - eg 10% of 10mm vs 10% of 100mm). You could also play with the clay body as they have different shrinkage rates.

Until it is dry. You don't want it wet and in the kiln (unless you candle the kiln to dry it out).

Thanks!

I'm not measuring density directly, but I do measure out the water when mixing up the glaze. I use 90% of the base weight in water.

Thanks! Glad you liked it.

I do think if you can brush on a layer that would help. The bristles can pop the air bubble. That is if your form allows it. As far a pressure, I worry about the 3d prints since they are mostly hollow.

Yep, and that didn't work for me.

Room temperature is fine. Actually what matters most in drying your pots is to do so evenly. If you do accelerate the drying you need to be rather careful so it doesn't crack during firing. Slow is much easier.

It's so useful!

I looked at PTFE on McMaster - and it was way too expensive. The problem is the quality of holes and therefore material needed.