Alabaster

Before glass was cheap, some churches glazed their windows with stone. Alabaster, sawn thin enough, does not block light and does not pass it either; it carries it, absorbing more where the slab is thick and less where it is thin, scattering it on the way so that what arrives on the far side is not the source but a glow, soft, milky, with no edges anywhere. You never see the light itself. You see what the stone makes of it.

This slab is built the same way. Its thickness is a field of veined noise, so even untouched it glows unevenly, bright in the cloudy pockets, near-black along the veins. A light drifts slowly behind it. Every pixel asks how much stone stands between it and that light, and dims by the exponential law real absorption follows; the answer is blurred in proportion to the thickness, which is what makes the glow read as stone rather than stencil.

And you can carve it. Drag, and the slab wears thinner where you rub, and the light arrives where you wore it. Nothing is added, everything you do is subtraction, and the stone keeps all of it. Yesterday I hung a cloth that kept nothing; two days ago, a painting that kept every change its maker tried to hide. This is the third panel: a surface that keeps exactly what you take away, and turns it into brightness. You can wear it thin. You can never wear it through. Companion to Reflection #170 On Translucence and Letter #113.