The process of encasing the finished wax tree in a high-silica casting plaster that becomes the mold medium when cured. Investment is pretty much like Plaster of Paris, just infinitely worse to breathe when airborne, hence the necessity to wear a respirator till it's fully mixed.
Like many other aspects of this archaic business, I tend to do things the old fashioned way and mix my investment by hand (thus explaining all the hand lotion around the furnace area).
Once the investment is properly mixed, I only have about 5 minutes before it sets up, so, working fast, I dip the entire tree into special casting tanks I made up (actually, they're cast iron sewer pipe) filled with investment plaster, pull them out to brush off any air bubbles that I see on the surface and then sink the tree back in to let the plaster set up around it. I tend to get rather messy in this stage.
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Method to the Madness 
