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The way we used to do it was to do a pour to cover your former, then the whole lot goes in the tank for vacuuming out the bubbles. (Obvs, the wider your tank the better)
Lego bricks sealed to a plastic base using plasticine, are useful for making a container into which you place your former prior to doing a pour.
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You would be surprised it’s quite easy to introduce bubbles.
Another way you can do it is to pour it slowly from a height in to the mold, like a long thread, the idea is that it is so long and thin that it breaks any bubbles. Does away with the vacuum chamber too.
Also might be worth considering painting the first layer on, very thinly then pouring over that. The bubbles only matter on the face of the object so it doesn’t translate when you cast things.
What ever you choose to do, it’s worth thinking it through several times, it seems like an easy way to duplicate things but it’s easy to make a mistake or not anticipate how it will work out when you go to cast things. For instance, I made a cast from a human skull and it looks good, but the top of the mold is where the face and scalp is, so all the little bubbles show up in the face and top of the head, whereas the underside is perfect, and that bit doesn’t matter…
Very cool, in my mind the act of pouring would be enough to agitate the mix and introduce bubbles but I guess it’s thick enough not to.
I learned something :)