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Best Way To Add A Bottom Base To A Slip Cast Object?

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HI all ,

What is the best way to create a base for my porcelain slip figures? Right now, I pour them and they are hollow and completely open at the base.

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- Would I need to buy actual clay to roll into a slab and attach to the bottom?
- Is there a simple way to add a bottom base using the liquid slip?

 

I am using Laguna porcelain slip, cone 6 for the figures.

I am self taught with ceramics so thanks for your patience!

 

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I've done some slip casting with Laguna slips. I'm largely self taught as well so don't feel bad! The tube in the picture does look very thick... you can pour off the slip sooner for a thinner product and it will still be fine.

 

What does your mold look like? Is it one or two pieces?

 

I think the easiest and best way to add a bottom would be with the slip, adding a piece to the mold or some other way. You can try a slab bottom but be aware that the shrinkage on the body and base must match up or it will crack away.

 

Another thing is, I don't know which glazes you're using, but I've had problems with Laguna slip cast items causing crazed glazes. Even their own glazes craze on the porcelain because the shrinkage doesn't match up.

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I had the base of a few chess pieces break after pouring. I set some of the slip on a plasterboard to thicken. I made a new base from the "slip clay" that had thickened. I put the base and the chess piece in a damp box for a week so the moisture content of the 2 pieces were the same. I then used slip to bond them together. It worked for me.

 

You could do the same. But make sure both pieces have same moisture content as you glue them together or they will crack. The damp box is a great tool for this.

 

Jed

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When I wanted to cast a hollow egg I found that the technique described in

Sasha Wardell's book Slipcasting worked well. [seen UK 2nd hand copies <£4.]

 

More details if you want them, but basically you

- fill your mould

- wait for the walls to form

- almost empty the mould

- add a plaster cap to the mould

- invert the mould and let the remaining slip complete the casting.

 

Two obvious caveats.

1. You may wish to prick a small hole to avoid the final form being air/steam-tight.

2. You may move from a 1-piece mould (containing a spare and trimming guides) 

     to a 3-piece mould (the main casting, a removable spare, a cap to replace the

     spare after initial trimming).

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Oops, I described a  slightly modified version of the process (which I used for a 6-up egg mould).

 

The original plugging method, as described by Sasha, consists of:

 

- make extra mould part to plug the spare [*]

- fill mould &  let cast-up

- drain & cut off the spare

- let harden up slightly  & add a small amount of extra slip

- insert plaster plug into spare & invert mould

- leave to cast-up the bottom (which may be thicker than walls)

- remove from mould & make discrete air-hole

 

* Ideally make this plug first (with finger-holes to aid removal)

  and use it to form the spare when casting the main mould.

 

 

 

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Oops, I described a  slightly modified version of the process (which I used for a 6-up egg mould).

 

The original plugging method, as described by Sasha, consists of:

 

- make extra mould part to plug the spare [*]

- fill mould &  let cast-up

- drain & cut off the spare

- let harden up slightly  & add a small amount of extra slip

- insert plaster plug into spare & invert mould

- leave to cast-up the bottom (which may be thicker than walls)

- remove from mould & make discrete air-hole

 

* Ideally make this plug first (with finger-holes to aid removal)

  and use it to form the spare when casting the main mould.

Thanks, PeterH, this is very helpful. Already picturing how to make a plaster plug for a finished commercial mold, WITH finger holes!

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