How can I dissolve dried plaster of paris?

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Discussion Overview

The discussion revolves around methods for dissolving dried plaster of Paris, particularly in the context of a project involving a scale model. Participants explore various techniques and considerations for effectively removing the material from a glass casserole dish.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that water and time will eventually dissolve the plaster, with the addition of acid or sugar potentially accelerating the process.
  • Another participant proposes converting the dihydrate form of plaster back to hemihydrate by heating it at 150F for several hours, which may help it crumble more easily.
  • A request for an estimate of the heating duration is made, leading to a response that suggests it could take 2-4 hours, but may extend to a day or more depending on the thickness of the plaster.
  • One participant expresses interest in using microwave heating, recommending a gradual increase in power during the process.

Areas of Agreement / Disagreement

Participants present multiple approaches to dissolving plaster of Paris, with no consensus on the best method or the exact duration required for heating. The discussion remains unresolved with competing views on the effectiveness of different techniques.

Contextual Notes

Participants mention various factors that could influence the effectiveness of the proposed methods, such as the thickness of the plaster and the specific conditions of heating, but these aspects remain unresolved.

ninapilapil
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My groupmates and I were using plaster of paris for our Arch 10 scale model of a chair. We used a glass casserole for the first trial. Kind of stupid. We covered it with oil before putting in the mixture but when the mixture dried, we couldn't get it out anymore. How can I dissolve plaster of paris?
 
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Water and time will eventually get it out. Acid or sugar will accelerate it somewhat.

You can convert the dihydrate back to the hemihydrate by baking it at 150F for several, perhaps many, hours. It should then crumble easily.
 
chemisttree said:
Water and time will eventually get it out. Acid or sugar will accelerate it somewhat.

You can convert the dihydrate back to the hemihydrate by baking it at 150F for several, perhaps many, hours. It should then crumble easily.

An estimate of how long?
 
ninapilapil said:
An estimate of how long?

For the heating step? It should take from 2-4 hours but depending on the maximum cross section the water must traverse on the way out, that could increase significantly... perhaps as much as a day or more.

http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1432.pdf"

http://cr4.globalspec.com/thread/25981/Gypsum-dehydration"

I like the idea of microwave heating. Heat slow at first and then ramp up the power.
 
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