The bowl over their heads stops providing shade. Now it's turned sideways, and the mirrored concave side is concentrating a lot of sunlight on a patch of clean sand well away from both of them.
“All right. You could claim the sand and then reshape it into glass, but that would take longer because instead of just glass, you have sand grains with air and dirt between them.”
The mirror is moving its focus along the sand, gradually adding on to the edges of a disk of fused sand. It's not exactly window glass, but at least it's melted smooth on the top.
“Yes, but you don't need to touch it with your hand, just touch it with the glass you already have, and once you are able to reshape it, you can cool it down quickly.”
“Take your glass and just poke the mess somewhere. Claim all the fused part, don't worry about anything that isn't easy; it'll break off.”
“Now that you have all of that glass, split the stick before where it gets hot and take back your original glass. You'll use that for an anchor point, so hang onto it or wrap it around you or stand on it.”
He gestures suggesting a semicircular arc over their heads.
“By the time it reaches the ground on the other side, it should have been cooled enough by the air that you can touch it.”
He walks over and touches it with a glass-covered hand (his glass, which is colorless), and then a bare one. She can feel his hand.
“All cooled off. You've got a couple kilograms of glass there, I think. You can do a lot with that if you don't actually need solid thickness in particular.”
“I mean, if you wanted to make a lens or something where you need there to actually be glass in the middle, or if it needed to be heavy. You can make reinforced hollow objects instead if you only need the shape.”
It'll be pretty awkward to plow the beach by pulling with one arm on a bracelet. Perhaps she should consider switching to a harness of some sort.
“It was just like this to cool off. Now you can reshape it into something sensibly compact and carry it however you like. And I don't mean to suggest that you should carry around exactly this much glass and more stuff on top of that; this is just for practice for now and you can decide what you want to do when you leave.”
A little work with “towards” will make it stay in a radius like an unenthusiastic leashed pet, and not roll away if she kicks it wrong.