Any idea what to use to make sure porcelain slip doesn't stick to aluminum press mold?

[art-ceramic nyc]

I am working with Porcelain slip and trying to cast it with an aluminum press mold I designed. Problem is the slip tends to stick and bond to the metal.

Anyone has any suggestion on what to apply to the metal to avoid it bonding to the slip cast? For plaster I used vaseline and it usually works.

[neilestrick]

Press molds are meant to be used with moist clay, not slip. To keep the clay from sticking to the metal you can use a thin coat of vegetable oil, which will burn off in the bisque firing. However, if you need to apply slips or underglazes before bisque firing, the oil will be a problem. In that case I would dust the clay with corn starch before pressing it into the mold.

Plaster molds can be used as a press mold with clay, or you can cast in them with slip. Either way, they should not be sealed with anything. The porosity of the plaster will dry the clay or slip and allow it to come loose from the mold after it sits for a bit. Once you've put vaseline on it, you'll probably never get it clean enough to be used for slip casting, though.

[Mark C.]

spray vegetable oil (pam or any brand name) but it will need to be bisqued to burn it off the clay

[PeterH]

1 hour ago, art-ceramic nyc said:

I am working with Porcelain slip and trying to cast it with an aluminum press mold I designed. Problem is the slip tends to stick and bond to the metal.

I may be misreading your question, but:

Casting slip needs to be cast in a porous mould (typically plaster) which sucks the water out of the slip. 

A press mould typically has a sheet of rolled out plastic clay pressed into it. The porous nature of many press moulds helps the pressed item dry (and hence both firm-up and shrink away from the mould).

 

What is the name (or recipe) of your porcelain slip, and can you explain what you are trying to do in more detail?

 

[Jeff Longtin]

Years ago I was watching an episode of "This Old House" when they highlighted the  process of manufacturing terra cotta planters. I was amazed when I saw that they were pressed molded using a metal mold. What allowed the clay to release from the metal mold was that the mold heated up and the water turned to steam. The steam allowed the pot to release easily from the mold.

I'm presuming heat is the missing ingredient in your situation. (Or you need to press when the clay is stiff and less prone to sticking?)