help needed re slip casting

[eoteceramics]

Hi All,

First time slip casting .

Ive mixed my own smooth earthenware slip to a creamy consistency and poured. I expected to leave for about an hour before removing the moulds, however after leaving overnight they are still too soft. Also there is a white mold growing on the plaster mould!. Could it be that they are too damp, I did have to clean with a damp sponge .

thanks so much Julia

 

 

[JohnnyK]

Hi Julia...

Were the molds dry before you poured the slip? The growing white mold may be an indication that the molds are too wet for casting. You can probably wipe the mold off the molds and treat them with bleach to reduce the recurrence in the future, but the molds have to be dry before casting.

Can you send pix?

JohnnyK

[eoteceramics]

Hey Johnny,

Im fairly sure the moulds were dry as they had been sitting in a shed for a few years, it seemed fairly waterproof. Ive looked up the mould thing and found that its overuse of sodium silicate seeped into the capillaries of the mold. This doesnt explain why the slip wasnt drying, it still isnt two days later!

I might try cleaning with bleach then drying off in the oven.

Cheers , Julia

[Min]

@eoteceramics, can you post your recipe? I think you have probably added too much deflocculant. 

You can just wipe those fuzzy salts off the plaster with a sponge, don't need bleach.

[eoteceramics]

Hi Min,

Thanks for responding. Obviously I havent a clue what Im doing as I dont have a reciepe!

I just mixed me regular clay with water until it was creamy.  Then sieved, it looked smooth and about right which is why I thought it must be the molds.

[Min]

Hi Julia,

Okay, so it's not too much deflocculant but not any at all that is the problem. There is just too much water in your slip. Casting slips contain far less water than a slip made with just clay and water and yet look just as fluid.

There is an article about using your claybody and turning it into a casting slip here, and a short explanation of mixing casting slips here. For red earthenware I would suggest using Darvan 811. It's easy to add too much deflocc so you need to be able to accurately measure the deflocc and slip as you find the right amount to use. (Some pugged claybodies don't work well as casting slips as there can be too much bentonite in them which causes them to cast too slowly.)

[eoteceramics]

18 hours ago, Min said:

Hi Julia,

Okay, so it's not too much deflocculant but not any at all that is the problem. There is just too much water in your slip. Casting slips contain far less water than a slip made with just clay and water and yet look just as fluid.

There is an article about using your claybody and turning it into a casting slip here, and a short explanation of mixing casting slips here. For red earthenware I would suggest using Darvan 811. It's easy to add too much deflocc so you need to be able to accurately measure the deflocc and slip as you find the right amount to use. (Some pugged claybodies don't work well as casting slips as there can be too much bentonite in them which causes them to cast too slowly.)

Min thanks so much for the information. Ill have a look at those links and hopefully get it sorted. Cant wait to get started!