Casting materials
Finding a substitute for Bentonite
You can find an easy substitute at any pottery materials supply house for Bentonite. Find someone near who makes pottery. Ask them where they buy raw materials. You can buy clay already cleaned and sieved fine. But it's easy to make it yourself.
Bentonite green sand mixes are just one of the many formulas that will work. Any fine sand mixed with clay, water, a binder [syrup or molasses] will work. There are many formulas out there. I've used motor oil instead of the syrup as a binder once upon a time.
Fine sand? Just run any common sand through meshes. Screen windows, flour sieves, whatever you can find to separate the finer parts. Beach sand works nicely.
Add just enough water so that when you squeeze it in your hand it holds the shape you make. Try for the least water needed. It should not drip excess water.
It's not rocket science and does not require hard to find materials. You are not casting like the pros where time/effort is money. You can always melt it and try over. Experiment with what you have locally --- thats part of the fun.
Olivine sand
The 'Olivine' sand mentioned is a man made sand from crushed rock. It is prefered as they can control the size of the grains during the crushing and it has very sharp edges so the clay can cling better. Thus it can be of a very fine texture and still have enough clay clinging to bind it for a good casting and still allow free passage of gases to flow through such as steam.
As you read on casting it has been done world wide from materials locally found often with natural occuring sands found on river banks.
There are many great books available both at libraries and online at google books, etc on these subjects.
Misc
- A light dusting of the mold with baby powder before casting helps a lot with surface finish.
