Does it matter what surface is under the aluminum when you write on it? When I try this I'll try some old "anti-static mat" that the electronics assemblers discarded at work. It's medium-soft.
If I didn't have that, I can't think what would be a good yielding surface. A stack of newspapers?
Have you ever tried to fill the groove with ink or paint? I suppose it would flake of smooth metal pretty fast.
Usually I use a white plastic mini-blind slat and write on it with a 0.9 mm mechanical pencil. A mechanical pencil is always sharp! The wide lead makes a darker mark and doesn't break as often under my clumsy fingers.
I cut them 1/2-wide or 1/3rd wide when labelling 6-packs in a 72-tray, or rows in propagation trays with 50 or 128 cells. The narrow plastic slats stand up like tiny tent-poles and support Saran Wrap off the surface of the soiless mix. It's cheaper than humidity domes for me since I have a roll of 18" plastic food film (that's a lifetime supply!)
