Re: steam defects-drying out plaster mold


Bramblebush ForumsFAQ

Posted by bruce paul fink on December 09, 1999 at 08:44:49:

In Reply to: steam defects-drying out plaster mold posted by Tim Moran on December 07, 1999 at 22:38:51:


It has been noted by someone that

"two hours on the forge can save you 20 minutes on the drawing board".

In this case "several days in the foundry can save you 20 minutes on the Artmetal Forum".

Just use the search engine located at :

and put in appropriate words to find some of the best detailed writing listed anywhere on the web.

I put in 'burnout' and it came up with 55 sites with many of them being multiple writings.

Try 'plaster investments' and see what comes up.

From what you write here I really could not tell what you have omitted or missed but would guess 2 things.


Plaster is NOT an investment but is just the dominate material in it. It is the binder mixed with about 40% to 60% sands and fillers. It in itself is not porous enough or strong enough to burnout at a high enough temperature without cracking up in many segments.


You have to remove BOTH the mechanical water (the largest amount of H2O)

and the chemical water which will otherwise be released later when the metal is poured in at the higher temperatures.

Thus the "burnout" which is for more than just removing the wax.

I burn out larger molds so use 900F over a 3 to 7 day period and ALWAYS start the process with a WET mold.

If it air dries before the burnout I re-wet it. Reason is because the water is a good heat conductor and helps to bring the temperature up evenly thus minimizing any cracking thus less flashing.

Your smaller molds would sound like they would take a 20 to 24 hour period (just a guess on my part) at 550 F or higher which is better. I say 550F because I have done it that low by using an old reclaimed kitchen oven OUTSIDE on repeated clean cycles. (It was junked before I started to do it and figured I would wear it out fully before it hit the trash). It worked several times but is not a system with the Good Housekeeping Seal. And definitely has to be done outside. Any burnt wax or acrid smell when done is TOO much and means you are not done yet. The molds I did at that lower temp had very little wax involved so that is pushing a low limit for your works.

I prefer a gas fired burner as they will keep a flame going to burn up any wax as it exits, while otherwise unburnt fumes are also semi eliminated at the same time.

Put 'kilns' in that Artmetal Search Engine.

Good luck


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