i think im going to get some from fondry101
"Green sand" is sand that is used while damp -- as opposed to baked sand, which has a binder that hardens when baked. Green sand can be quite simple. The sand should be sharp, not rounded, so it interlocks together well. Should be around 100-150 mesh or so. The binder for green sand can be bentonite (about 5%) or fireclay (around 10%) but must be very fine, -325 mesh or finer. If there's a pottery supply place nearby, the sand ("silica") and clay can be purchased inexpensively in 50 lb sacks. The two dry ingredients are mixed thoroughly by sieving them repeatedly through window screen. Then water is added via a sprinkler can and mixed in thoroughly. Just enough water is added so that the sand will hold together when squeezed and breaks cleanly into two pieces when broken. Although there are numerous additives that improve various features of the sand, this simple recipe is sufficient for 90% or more of home casting. Oil bonded sand is easier to use but harder to find ingredients. A lot of amateurs just bite the bullet and buy the oil bonded sand already prepared. Good luck!
Casting sand is usually a soft round sand mixed with bentonite.You will find a variety of formulas on the web if you search for casting sand formula.A cheap source of bentonite is Kitty litter Most casting sands are moistened with either water or oil just very small amounts to hold it together.http://www.cnczone.com/forums/casting_metals/42892-oil-bonded_green_sand_recipe.html
I was going to say its sand with a high clay content, I didn't realise it was Bentonite.
There are almost as many "recipes" as there are metal casters. :-) but Bentonite features in most of them.In general you may as well buy 25 KG of commercial sand - initially it will work for you until you gather the skills to :1. make a decent pattern2. Pack the cope and Drag properly3. Get to remove the pattern without the mould collapsing4. Pour the metal - a lot harder then it looks.We had a 5 kg casting furnace at school but because of H&S we only tried it in the evenings to see if it all worked. Never did get permission to use it when the students were there. I knew some schools that did but largely they had done this for years and no one every asked difficult questions
I think we should emphasise NOT TO USE WET sand. I think oil binders are used these days.
WET NO NO NOOriginally it was made just damp enough to hold together but as you say oil binders are used today.Playing with molten metal is fraught with danger for the amateur. The correct protective clothing and equipment are essential. Experience with someone who has done it before - a lot!
www.backyardmetalcasting.com and the sister site www.alloyavenue.com can give you all you need to start a home foundry on the cheap
I don't know about cost but there is a special sand called casting sand. Try searching on google.