Soldering with sun and a magnifier glass is possible, I think. CMIIW, but I don't think tin moulding using that technique is possible, at least if I compared it to modern solder wire. Once the tin get some small distance from the heat source, it just quickly change from liquid to solid, but not enough to get it into shape like that. If the mould is mounted vertical instead of horizontal, it might has a little better chance.