I couldn’t agree with Dan more, sand casting takes some experimentation and tinkering. Once you get your sand and flasks working, it’s a snap, but you will mess up a lot of casts before you get everything tuned. His tip for using cat litter as bentonite clay is pure genius, but be prepared to test several brands before you hit on one that works for you. Clay cat litter can be made from almost any clay. Sodium Bentonite (or western bentonite) is often chosen for it’s absorbency, but any given brand of kitty litter may vary between lots. “Bentonite Clay” can be either sodium bentonite, or calcium bentonite. They both work for green sand, but they have distinctly different qualities. Other clays can also work well for lead, pewter, or even aluminum casting, but won’t hold up to high temperatures very well. Wal-Mart used to have a cheap store brand cat litter labeled “bentonite clay” that I believe was almost 100% sodium bentonite: ‘Special Kitty’, sold for a few dollars in a 25 pound bag. It works very well for aluminum, copper, bronze and brass. I believe it would hold up with cast iron, but I haven’t tried it yet.
Before you start making your own green sand, It might be worthwhile to check around in nearby cities and look for a commercial foundry. (They are pretty rare, but a lot of cites still have one). A lot of founders are friendly and eager to help a beginner get started. A lot of them will sell you used green sand for very little if you will haul it away. They may also sell you “southern” (calcium bentonite) or “western” (sodium bentonite) bentonite clay or fireclay (used to make your furnace), cheaper than you can find them on line. They may also have a wealth of good advice. As a beginner, it’s really nice to get a look at a working foundry and see what “right” should look like. Check out their safety precautions while you are at it.
Be careful of breathing dust and fumes from your foundry. Melting metal puts out some nasty chemicals and mixing sands can raise clouds of dust. Great article! V/R, – JIR