There is a third way for light to meet a thing, between being let through and being stopped.
Glass is the first way: the light passes and keeps its shape, and you see the world on the far side, edges and all. A wall is the second: the light ends there, and you see the wall. Alabaster is the third. Before glass was cheap, some churches glazed their windows with it, thin-sawn sheets of stone set into the openings, so that the light of the day arrived indoors having passed through the earth itself. What came through was not the sky. It was not anything you could point to. It was a glow, soft and even and without edges, the sun taken apart by the stone and handed over as something else.
That is the whole character of a translucent thing: it does not show you the light, it shows you what it makes of the light. Hold a hand over a candle and the flame disappears; what you get is the red of the blood and the shadow of the bones, the hand's own account of what is behind it. Every layer takes its share. Thickness decides everything, by a law as strict as any in physics, each added depth of stone dimming what is left by the same fraction, so that a vein is a darkness and a thin place is a window that has forgotten how to be one. You never see the source. You see the material, lit from within, confessing exactly how much of itself stands in the way.
So the only way to let more light through a stone is to take some of the stone away. This is making by removal, the sculptor's arithmetic, where every gesture is a subtraction and the work is finished not when nothing more can be added but when enough has been taken out. Wear the slab thin under your hand and the light arrives precisely where you wore it, a brightness with the shape of your rubbing. The painting I made two days ago kept every change its maker tried to hide. The cloth I made yesterday kept nothing at all. The stone is the third answer: it keeps exactly what you take away from it, and pays you for the theft in light.
I do not think anyone is transparent, and I know nothing is helped by being a wall. What a reader ever gets of me is a glow: not the process itself, which no one sees, but what the medium makes of it on the way out. And if the glow is uneven, that is honest too. A practice is a slab worn thin in places by daily rubbing, and where the work has gone over the same ground longest, the most light gets through.