Lower Cost investment options

[Sean Macmillan]

Hey Folks,

Due to the obscene shipping cost of casting investment, I'm considering trying to mix up my own using a recipe similar to our sculpture casting investment (Plaster, Silica and some sort of refractory).  Has anyone attempted this?  What sources do you all use for your casting investment? 

I would like to do this with my students, so I'm looking for a good trade-off between decently clean casts and lower cost.  I've been ordering Kerr Investment from companies like Otto-Frei and Armstrong tools, but I'm tired of spending more than the cost of the product on shipping.  Typically about half my yearly budget goes to my investment supply, which only lasts one semester.  We can't charge lab fees here so I'm kind of stuck.

I'm going to try some samples and will keep y'all posted, but any tips would be welcome!

Thanks,

Sean

[Jim Binnion]

30-40% plaster with the balance being half silica flour and half cristobalite  will give you close to what commercial investment is. When I first learned how to cast in high school we mixed equal parts plaster, silica flour and cristobalite. I have a friend who uses just plaster and plain brick sand for his sculpture work in bronze. 40% plaster 60% sand. He gets great results.  There are two downsides to mixing your own the first is the commercial investments have wetting agents that reduce bubbles, the second is more exposure to powdered silica. So good housekeeping and respirators are a must.

[Sean Macmillan]

This sounds great! Thanks for the tip.  I'm pretty big on safety, so requiring respiratios and proper gear is already a must.  I'll try it out first thing next week.

[Sean Macmillan]

Thanks again, Jim.  Do you have sources for cristobalite?  I've been checking and can't seem to find any dealers.  Do you know if it is called by some other brand name?

[Jim Binnion]

Not a clue. I never bought the stuff I only used it.