I have been experimenting with aluminium plate etching and aquatinting at home. I use a copper sulphate and salt solution as the etchant, which is a lot safer than the acids traditionally used.
Aquatinting requires the printmaker to stop out (protect) parts of the plate from the etchant, in order to create a range of tonal values. I have tried a few different products, including traditional Brunswick Black (gloopy unless diluted with white spirit, which is smelly; slow drying; requires white spirit to remove), Lascaux Stop-out Resist (pleasant to use, but very hard to remove, especially from previously-etched areas) and Speedball Screenfiller. The latter has no smell, behaves like paint, and can be removed with just hot water and detergent. It also dries quickly and has good etch resistance - my favourite so far!
It can be difficult to judge etching times, as the etchant becomes less effective every time it is used. When using a fresh etchant, I would start with 20 seconds for the lightest midtone. For the darkest dark, the plate should be immersed for a total of 5 minutes. In the video below, I etched the plate for 20 seconds, 40 seconds, 80 seconds and 160 seconds.