What is plaster:
Plaster comes from a naturally occurring mineral state. Pottery Plaster #1 is a Gypsum based plaster.
When it is heated to about 300 degrees f it becomes a powder. The water of crystallization has been removed.
When you re-hydrate the material, the molecules are able to take up this water, and form new inter-locking crystals. This we recognize as set plaster. These interlocking crystals are a chemical reaction and create a sponge like quality that work to absorb the moister from clay.
Heat and cold will break down this structure.
In order for plaster to have the relationship with clay that we want, it is important that it is mixed in a way that the correct crystalline structure is developed.
To Mix:
Make sure the plaster feels soft and powdery (if there are hard lumps it may have been exposed to moisture)
Measure a little less water then you think will fill up the area you want to cover
Slake the plaster into the water, not too slow, not too fast-breaking up any lumps as you go
watch for the chemical reaction to occur where the plaster starts to sit on the surface of the water (not just a lump in the middle of the plaster)
Let plaster sit in water 2-3 minutes
Agitate until you can see a finger trail in the slip that disappears quickly
Mist with rubbing Alcohol to pop bubbles
Pour steadily into your mold, trying not to create air bubbles
Agitate the mold
Mist with rubbing Alcohol to pop bubbles
You can release carefully when warm or after warmth has cooled (anywhere from 20 min- 1hour)
Wet sand to clean up and compress plaster.
Plaster comes from a naturally occurring mineral state. Pottery Plaster #1 is a Gypsum based plaster.
When it is heated to about 300 degrees f it becomes a powder. The water of crystallization has been removed.
When you re-hydrate the material, the molecules are able to take up this water, and form new inter-locking crystals. This we recognize as set plaster. These interlocking crystals are a chemical reaction and create a sponge like quality that work to absorb the moister from clay.
Heat and cold will break down this structure.
In order for plaster to have the relationship with clay that we want, it is important that it is mixed in a way that the correct crystalline structure is developed.
To Mix:
Make sure the plaster feels soft and powdery (if there are hard lumps it may have been exposed to moisture)
Measure a little less water then you think will fill up the area you want to cover
Slake the plaster into the water, not too slow, not too fast-breaking up any lumps as you go
watch for the chemical reaction to occur where the plaster starts to sit on the surface of the water (not just a lump in the middle of the plaster)
Let plaster sit in water 2-3 minutes
Agitate until you can see a finger trail in the slip that disappears quickly
Mist with rubbing Alcohol to pop bubbles
Pour steadily into your mold, trying not to create air bubbles
Agitate the mold
Mist with rubbing Alcohol to pop bubbles
You can release carefully when warm or after warmth has cooled (anywhere from 20 min- 1hour)
Wet sand to clean up and compress plaster.
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