Expert: Sam Kelly - 7/12/2008

Question
I am using slip low fire for ceramic figurine i problem is
when i remove from mold the back sinks in i have tried thicker slip also thinner slip some problem i also put talc
powder very lightly in mold I did lots of pouring 2 years just out of touch thank you for any help LaDonna

Answer
How old is the mold and is it in working condition. Get another mold and cast a piece from it and see if the same thing happens.

Are you leaving the figurine in the mould long enough for it to set, unless there is a reason to take it out as soon as possible leave it in the mold for a longer time. If you have already done this the problem of:
1)slow casting can be corrected by decreasing water addition or decrease dispex addition to your mix.
2)Flabbiness which means it's difficult to handle without distorting it is corrected by increasing dispex addition to your mix

Where is the slip from, if you are making your own I would make another lot just to make sure I mixed it correctly.

Deflocculants:
The amounts of Sodium Silicate or Dispex N40 added to a casting slip are very critical and too much or too little may each result in the slip being too thick. If this happens, take a 1 litre sample of the slip and add one or two drops of Dispex N40. If the slip becomes thinner after stirring then this shows that more is required to achieve good fluidity. If the slip becomes thicker then this shows that too much has been added already. Therefore more clay and water needs to be mixed into the slip in the same proportion as given in the casting recipe – no more Sodium Silicate or Dispex N40. The recipe can depend on the quality of the water supply, which may vary from one location to another and also may be affected by minor variations in the body’s raw materials.

Sam