Markus Kayser uses Sahara sun to sinter (melt and fuse) sand in a layered technique like 3D printing to produce glass objects. He gives a talk and explanation in his TEDx talk. If you subscribe to his YouTube channel , you will see his other sun-cutter video. In Bang Goes the Theory these guys use focused sunlight to melt rock at 3,500 Celsius: "Just two square metres of sunlight can melt steel easily"
HackerMaker is the culture and philosophy of creating, repairing and inventing out of whatever is available. Raw materials are no longer the raw materials with which we work. Our prime materials have been extracted, cooked, processed, moulded and shaped cheaply and in large qualities to fit some purpose other than ours.