saw ya (commented?) on the vid(s).
Lota fun there, here too.
As U no, been waitin for this. Did some of it in the 70s (artist forge).
I don't think we used green sand. Here's a 2nd material. I'm betting we
used a 3rd:
We are using Petrobond, a so-called "oil bond sand" that is made from fine silica sand, clay, and mineral oil. The clay, wetted with oil, acts as a binder and gives the sand strength once it is compacted. The alternative to oil bonded sands are "green sands", which are formed from sand, clay, water, wood flour, and a few other ingredients. Oil sands are stronger, require less maintenance, and are generally easier to use, but are more expensive, and require petroleum products. Green sands are cheaper, and can be made DIY, but they require more maintenance, since the water will evaporate out.
If interested I'll get more info