Slip sticking to molds?

[Elmoclayman]

I have been making slip castings of some mugs with Tiki style face carved in them. I made sure to have no undercuts so that they would release from the mold. I had a Cone 10 clay body (Soldate 60, for those familiar with this body) that I was using to make slip from and it seemed to be working just fine. I started using a store bought Cone 06 Clay body that has no grog so I could get a smoother result and also use the brighter colors of the low fire glazes.

 

My problem is that I am having difficult with the leather hard slip releasing from the mold. The molds are 4 piece molds and made from the same plaster that I was using with the Soldate 60 and having no sticking problem.

 

Any suggestions would be welcomed.

Brian

[Marcia Selsor]

Have you given them time to dry somewhat?

 

Marcia

[Elmoclayman]

Have you given them time to dry somewhat?

 

Marcia

 

 

I have tried letting them dry over night, and that didn't work. The details caused it to crack and tear itself apart. I have also tried letting them dry for about 1 hour until the slip was leather hard, or slightly beyond, and still they stick.

 

Is just a matter of finding the ideal drying time through trial and error?

[neilestrick]

Are you deflocculating the slip? Is the mold dry and clean?

[Elmoclayman]

Are you deflocculating the slip? Is the mold dry and clean?

 

 

I have mixed the slip according to the manufacturers specs. With a specific gravity of 1.76. I have tried 1.79 and also 1.72 spec. gravity and have been having similar results.

 

The Slip does tend to "settle" or dry quickly. If I leave it for an hour or so, there is more firm "skin" layer that develops on the surface, usually about 1/2" thick. I just mix that in to the slip and strain it before pouring and it doesn't seem to be effecting the consistency of the slip.

 

The molds are dry and slightly warm to the touch, similar to a bone dry piece of clay. Perhaps I need to leave them dry for longer than 24 hours. The humidity has been a little hi over here in Southern Calif.

 

I am fairly new to slip casting, so any advice is appreciated.

[neilestrick]

What deflocculant are you using? Sodium silicate? All clay bodies deflocculate differently, depending on what's in them. So a general casting slip recipe won't necessarily be correct for your clay body. It'll take some tweaking. I would first try drying out the molds better, then stiffen up the slip.

[Elmoclayman]

What deflocculant are you using? Sodium silicate? All clay bodies deflocculate differently, depending on what's in them. So a general casting slip recipe won't necessarily be correct for your clay body. It'll take some tweaking. I would first try drying out the molds better, then stiffen up the slip.

 

 

Been using Sodium Silicat mixed 50/50 with water, per the manufacturers directions.

[Mark C.]

To aid in drying the modls some air moving over them (small fan) really works great.

I would dry them better and spend some time tuning the slip-Hydrometer and slip cup are two tools you need as well as a timer for the slip cup. Read up on this

I would in the future use darvon 7 instead of sod sil.

Laguna clay sells it as well and as you live in So cal thats easy.

If you are sure the slip is mixed right and its sticking still its wet molds or undercuts. If you are not sure about your slip you will need to get that right 1st.

If the rough clay body worked on the mold so will a fine body so My guess is wet mold and slip not right yet as Neil says needs tweaking.

Mark

[neilestrick]

I've had really good luck with this recipe from the Laguna website. However, for clay bodies with low clay content, like porcelain or white earthenware, this recipe has too much water per pound of clay. I would start by mixing all the diluted sodium silicate and soda ash with all the water, then add about 1/2 the water/sodsil solution to the dry clay and mix well. Then add the water solution bit by bit till you get the proper viscosity. The barium is really only necessary for terra cotta slips.