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Using a vacuum formed sheet to release clay from a plaster mold


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Has anyone used a sheet of plastic, that has been vacuum formed to the shape of a plaster mould, as a way of quickly removing clay that has been pressed into it? Im keen to find alternative ways of releasing the clay quickly on my homemade ram press. I live in the UK and sourcing the materials to make an air release mould is very pricey and difficult. If anyone knows whether the idea above would work or has an alternative suggestion, I would really appreciate the help!

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Why not try it with just a piece of plastic like plastic bag just to see what happens. Seems like to me that the press removes water, and if you have plastic to keep the water from draining it may be a problem. just thinking.

 

best,

Pres

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11 minutes ago, Pres said:

Why not try it with just a piece of plastic like plastic bag just to see what happens. Seems like to me that the press removes water, and if you have plastic to keep the water from draining it may be a problem. just thinking.

 

best,

Pres

Thanks, Pres, you have given me an idea - I will make plaster moulds of plastic cups, and then use another plastic cup as a sleeve that can sit between the mould and the clay. I will get back to you on how it goes.

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I think if you use a plastic mold or mold liner, you would have to spray it or wipe it with some sort of mold release to remove your clay object quickly since the plastic will not absorb water...I don't know if the mold release would cause problems with the clay afterwards. On your second thought about using the plastic cup as a liner...why not just use the plastic liner as your original mold? That would save the step of making a mold of the plastic cup...

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I've been using a layer of plastic food cling wrap as a release agent on my hump molds.  The super thin plastic leaves no impression apparent to me on the clay.  It sticks to the clay but releases without issue from the mold itself.  This technique really perfects hump molds IMO.  I can form the body, add feet, textures, and a rim, immediately turn it over, remove the mold  and finish the inside.  Cling wrap is available in 18 inch widths.

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29 minutes ago, CactusPots said:

I've been using a layer of plastic food cling wrap as a release agent on my hump molds.  The super thin plastic leaves no impression apparent to me on the clay.  It sticks to the clay but releases without issue from the mold itself.  This technique really perfects hump molds IMO.  I can form the body, add feet, textures, and a rim, immediately turn it over, remove the mold  and finish the inside.  Cling wrap is available in 18 inch widths.

Thanks CactusPots. What do you mould on your hump moulds? I am trying to mould mugs and I imagine that cling wrap leaves marks where it creases and folds over itself. If I was moulding something like a plate or a bowl, I could see this working really well. 

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A length of sheer pantyhose stretched tight works well as a barrier. Pull it taunt and hold it in place with rubber bands or duct tape on the inside or underside. Doesn't seal off the mold the way plastic film does so some moisture can still escape, clay releases easily from it.

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I make planters primarily for cactus and succulent collectors.  So my molds are mostly round or oval.  From about a cereal bowl up to a wash basin in size.  Other techniques for other shapes. 

Panty hose would work ok for smaller pieces.  I tried a fabric called "4 way stretch" from a basic fabric shop.  It moves like panty hose fabric, but you can get it in yard lengths.    It works ok if you can pull it tight and pin it securely to the mold.   I have it on a large round styrofoam mold with lots of thumb tacks.  Too hard to get all the creases out on anything but a round mold.  It does work great.

The cling wrap is so very thin, I can't see any marks on the clay even when I'm not careful to get the overlaps of the plastic out.  Mugs are so small, I'd question hump or slump molds as a viable option, unless you're talking pour molds.

I want the mold out as soon as possible.  The work has to stand on it's own feet as soon as the outside is finished, so I can work on the rim and inside fresh.

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