Reducing Bubbles in Plaster Slip Casting Molds

Рет қаралды 4,600

Жыл бұрын

How can we reduce bubbles in plaster? In this video I try 3 different things. The first is windex on my silicone mold. This is supposed to help with surface bubbles and seems rather effective! The second is a different type of mixer for the plaster. This one doesnt move the plaster up or down pulling in air and instead slings it out to the side. I think this also helped. Finally I found an old industrial shaker table and try it out. The ideas is as it shakes the bubbles will rise to the surface. It also seemed to help. However! I still had bubbles, but only under horizontal surfaces. So I think my silicone mold is capturing them and preventing them from escaping. This will like require redesigning my molds in the future.

Пікірлер: 28

@katelyngettner34 Жыл бұрын

In school we would tap the bucket holding the plaster after mixing and before pouring to agitate the bubbles to the surface. Then you can swirl the liquid to group the bubbles that have come to the surface and skim them out before pouring. We also pour to the side of the mold interior directly onto the palm of a hand touching the side of the mold so the plaster kind of just slides in so as to avoid any additional bubbles collecting along the form of the body you're casting. As a last step we would pound on the table to float the remaining bubbles up or you can stick a hand in the liquid plaster right at the surface and kind of just bounce it to agitate the liquid lightly and bring the bubbles up. Granted the way you're casting the mold is pretty different from any way I've ever done. If you're making simple drop molds you can actually just throw a solid form on the wheel upside down (so think the lip of the form would be what is attached to your wheel head, and you would be defining the foot at the top) and then throw your cottle walls out of clay around the exterior and cast directly into that. Ceramic Jim has a video that's exactly that kzfaq.info/get/bejne/bdRnrbhhp8DXfKs.html although it occurs to me just now that your might not have a wheel. Either way you're going to want to make sure you get all your bubbles out before inserting the top silicone piece as that is most likely a recipe for catching those surface air bubbles.

@PotterybyKent Жыл бұрын

Thanks for the tips. Yes you're correct in that I don't have a wheel. And while this mold is rather simple (it's actually one of my older!), I have made much more complex ones using 3d printing, or as in my last video with legos! But related to your point, the advantage of doing it upside down is the same as what I mention at the end - the bubbles will rise away from the surface which forms the pot.

@Bob-Is-A-PotterNow Жыл бұрын

For another purpose, I ordered a 5 gallon vacuum pot which is supposed to arrive tomorrow. I'm going to see how that works (intent is similar to epoxies and silicon).

@PotterybyKent Жыл бұрын

A vacuum pot would likely work very well. A pressure pot might as well (collapsing the bubbles). I've been keeping an eye out to see if I can find a good deal on one myself. The shaker table came up first though!

@Bob-Is-A-PotterNow Жыл бұрын

@@PotterybyKent I'll let you know how it goes. I've been thinking about making my own shaker table, as it should be fairly simple and I've got a variety of microprocessors to play with and choose from as well as stepper motors. Ah, the joys of being ADHD! 🙃

@PotterybyKent Жыл бұрын

Always so many projects to pick from! But I wouldn't have it any other way. I'd thought about making my own until I found this one. One thing I quickly noted in the video that might come in handy in thinking about a DIY version is that this thing is heavy! It's about 15lbs and I suspect that mass is useful for this kind of low frequency operation.

@Bob-Is-A-PotterNow Жыл бұрын

@@PotterybyKent Good point regarding mass. Especially since I was thinking to be able to handle a five gallon bucket! I think I'll need to think about how to clamp the whole thing down. May need to cast a pretty massive plaster of paris base with mounts.

@Bob-Is-A-PotterNow Жыл бұрын

The vacuum pot arrived last night. Today I made a casting of a plastic supermarket snap-together food container that I liked the contours of. My initial plan was to place the container upside down and stabilize it with modeling clay, which I did. But as I was going to place everything in the pot I realized pulling a vacuum on the mold would expand it, pop it free to float to the surface, or both. What I did instead was after gently mixing the PoP with a drill motor, I put the PoP in the vacuum chamber for about 10 minutes and pulled 25" of mercury vacuum - about -12 psi, which here near Denver, where the normal atmospheric pressure is about 12 psi, equates to a decent level of vacuum. This created a foam of giant bubbles, which I gently shook and swirled. (It was really interesting to see how much the batch swelled under vacuum - at least an inch, if not more). I then carefully poured the batch through a kitchen strainer. The result is excellent, not a bubble anywhere. There is a rough surface in a couple of spots, but that was due to not getting my liquid soap release agent distributed well. Overall, very, very pleased. I will repeat the process tomorrow with a couple of other mold masters and this time I'll video the experience and post to my youtube channel. The vacuum pot is a winner for me!!!!🥰🤩😁👍

@Daall-kw7hm 9 ай бұрын

Or is there any way to make vibrate table on my own ?

@PotterybyKent 9 ай бұрын

I'd imagine so

@Daall-kw7hm 9 ай бұрын

From where to get the vibrate table ?

@PotterybyKent 9 ай бұрын

I got mine at a local auction

@hannesaltenfelder4302 Ай бұрын

Maybe if you put a long straw in the middle of the inner plug the air underneath can escape?

@PotterybyKent Ай бұрын

Plaster would likely just fill it up. Changing the pouring orientation has proven to work pretty well.

@galetine5253 5 ай бұрын

Pour the plaster over the item and then shake it so the bubbles rise away from the item you’re moulding instead of into it

@simoncroatia Жыл бұрын

I made 2 molds the other day and I'm very unscientific about the whole process. What I did find is that the mould with the thicker plaster had much fewer bubbles and the wetter plaster mold had quiet a lot.

@PotterybyKent Жыл бұрын

Maybe the more watery one foamed more in mixing? There are a ton of different variables at play for sure! The other difference with thicker vs runnier is the strength of the resulting plaster. The other video I mentioned in passing about testing paster mixes actually resulted from me being unhappy with a wetter plaster that ended up too soft once set.

@keesstaps4606 2 ай бұрын

Try methylated spirits

@PotterybyKent 2 ай бұрын

What the chemistry behind that approach?

@gonenhaba-meishar1288 Жыл бұрын

i saw some people use alcohol to fight the air bubbles - but i cant think of any scientific explanation

@PotterybyKent Жыл бұрын

Great point - I've seen similar usage as well. People will spray alcohol onto the top surface of the plaster while it is still wet to break bubbles. I think what is going on is the alcohol breaks the surface tension of any bubbles floating on the top. The way my mold is set up, that top surface is tiny (the gap between the two pieces of silicone). It also not part of the pot (slip will never touch that surface) and by the time I secured the inner mold, it was rather hard to access the wet plaster from above. So I didn't do it. If I had a mold with a larger open top surface (and/or I was concerned about the non-pot sides of the mold) it could be worth a try. I also wonder if a spray of windex would work similarly - since I already have it out.

@charlottesmom Жыл бұрын

I used to make soap, we always sprayed the soap with alcohol after pouring and the bubble magically vanished. I hope it is as easy with plaster. 👍🏻

@firstenforemost Жыл бұрын

I think all of your problems would be solved by not trying to create a mold right-side-up. The important surface is the inside of the mold, not the surface that touches the outer container you hold everything in. I'd put the smaller silicone master and the form it sits in upside down, glued to a surface, then put a round tube around it that's tall enough, and glue that down. Then just pour the plaster in over the pot and vibrate. Bubbles will rise AWAY FROM the form, instead of upward against it.

@PotterybyKent Жыл бұрын

Thanks! You are correct and that is exactly the next video I did. While it didn't address all of my issues it did indeed help. Let gravity be your friend!

@razorSH 3 ай бұрын

You are introducing too much air due to the way you are mixing the plaster. The entire mixer paddle needs to be deeply submerged at all times during mixing in order to not let any air into the plaster. You need either smaller mixing paddle or taller container and to keep the paddle as close to the bottom as possible

@PotterybyKent 3 ай бұрын

Yep. I talk about this more in more recent videos. A bit counterintuitively, mixing more plaster is easier in this regard.