Looks like pewter to me. I doubt it was residue crayon that lost detail but the need of lubricant to aid the pewters flow. I wonder if puffing talc into the mold and blowing out the excess would help with detail. I have not worked with sand etc, only silicone.
Before I bought Italian Fine Talc, I was using the cheapest dollar store stuff I could find with almost no fragrance and a kind of tan in color. My molds are silicone and I get bubbled surface without a lubricant in gravity casting. Pressure casing I do best with naked silicone, but speed is a difficult thing as my pressure tank is CO2 and simply rather cool so getting it in the tank, tightening the lid and turning releasing the valve before the pewter solidifies can be a trick.
Your images are very small so I really can not see the details before and after. At least 640x480 images will fit on anybodies screen. Perhaps you could upload images double whatever resolution you already have in the future? The forum system accepts larger images. Also the macro switch on your camera for close ups is helpful if you are not already using it. The macro button is shaped like a flower. Between that and suppressing the flash (lightning button on my Cannon) and I can get in real close.
I dig you like working n crayon. There is a lot of fine work done in soap around the world by prisoners. When you get a few extra bucks you might try the following. I suspect that you would love Matt wax, perhaps their softest "Blue," grade as you can bend it more before it breaks. Some folks heat the sculpting tool, dental pick etc over an alcohol lamp and sculpt that way, I often use a Dremel like device with tiny metal burs to rough in the shape. You can drill it, hack saw it, chip carve etc. Just a thought. I do realize jewelers waxes can be terribly confusing at first as their are so many grades and brands. But you might be surprised just how much use and reuse you can get out of the stuff. Until you have exactly what you want to "lost wax," the final sculpt.
Matt Wax is very pure, bubble free and slightly translucent. This helps when sculpting a thin section. It can be made opaque with Mason Ceramic Stains and even change its color.
3-1/8" x 1-7/16" (79.38 x 36.5mm) slices; thickness varies; 1-lb. (2.2kg) box of blue wax
www.riogrande.com/MemberArea/ProductPage.aspx?assetName=700516&page=GRID&category|category_root|122=Casting+Equipment+and+Supplies&category|cat_122|362=Design+and+Model+Making&category|cat_362|4518=Wax+and+Wax+Working&category|cat_4518|4522=Carving+Wax&first_answer=31
Anyhow, I am glad your experiment worked out for the most part.
Blobber
I broke this little guys legs so i though it would be a good first one to try as it is useless as a crayon now.
