Plaster formula with increased porosity
In one aspect, a pottery plaster formulation with increased water absorption, comprising alpha stucco, continuously-calcined-in-a-kettle stucco, and a combination of Rochelle salt and one or more of the following: potassium sulfate and/or a phosphate compound. In another aspect, pottery plaster molds with increased water absorption and methods of making and using the pottery plaster molds for slip casting ceramic items.
1 . A pottery plaster composition, wherein the pottery plaster composition is a dry mixture consisting of:
5-40 wt % alpha-calcined stucco;
60-94 wt % continuously-calcined-in-a-kettle (CCK) stucco;
0.02-0.2 wt % Rochelle salt; and
0.05-0.5 wt % at least one of the following: potassium sulfate and/or one or more phosphate compounds; and wherein the pottery plaster composition has a water absorption capacity of at least 10 wt %, calculated as an increase in pottery plaster weight measured in the full immersion test at 60 minutes.
2 . The pottery plaster composition of claim 1 , wherein the phosphate compound includes one or more of a trimetaphosphate salt and/or a tetrametaphosphate salt.
3 . The pottery plaster composition of claim 1 , wherein the pottery plaster composition consists of:
15-30 wt % alpha-calcined stucco;
70-84 wt % CCK stucco;
0.02-0.1 wt % Rochelle Salt; and
0.05-0.3 wt % potassium sulfate.
4 . The pottery plaster composition of claim 1 , wherein the pottery plaster composition has a shelf-life of at least 6 months.
5 . The pottery plaster composition of claim 1 , having the water absorption capacity of at least 25 wt %, calculated as an increase in pottery plaster weight measured in the full immersion test at 60 minutes.
6 . The pottery plaster composition of claim 5 , having the water absorption capacity of at least 30 wt %, calculated as an increase in pottery plaster weight measured in the full immersion test at 60 minutes.
7 . A pottery plaster slurry comprising the pottery plaster composition of claim 1 and water, wherein the pottery plaster slurry has a water to alpha-calcined and CCK stuccos ratio by weight in the range from about 0.5 to about 0.9.
8 . The pottery plaster slurry of claim 7 , wherein the pottery plaster slurry further comprises a set-retarding agent.
9 . The pottery plaster slurry of claim 8 , wherein the set retarding agent is used in an amount from about 0.1 wt % to about 5 wt %, based on a weight of the pottery plaster composition.
10 . A method of making a pottery plaster mold, the method comprising:
i) mixing a pottery plaster slurry comprising the pottery plaster composition of claim 1 and water into a mixture;
ii) pouring the mixture into a form; and
iii) removing the pottery plaster mold from the form after the mixture hardened.
11 . The method of claim 10 , wherein the mixture has a water to alpha-calcined and CCK stucco ratio by weight in the range from about 0.5 to about 0.9.
12 . The method of claim 10 , wherein the method further comprises adding to the mixture in step i) one or more set-retarding agents.
13 . A method for slip casting a ceramic article, the method comprising:
i) preparing a clay slip;
ii) pouring the clay slip into a pottery plaster mold, wherein the pottery plaster mold comprises the pottery plaster composition of claim 1 ;
iv) casting a ceramic article in the pottery plaster mold; and
v) removing the ceramic article from the pottery plaster mold.
14 . The method of claim 13 , wherein the casting includes removing water from the casting ceramic article under negative pressure applied to the pottery plaster mold.
15 . The method of claim 13 , wherein the method further comprises drying the pottery plaster mold after step v).
16 . The method of claim 15 , wherein the method further comprises repeating steps i) to v) at least once.