Andy said

What would we do without all this wonderful H & S legislation!

I used to use some stuff called Amonium Bi-flouride in 1960. I used it to
etch crystals for SSB filters etc. You could buy it from any chemist
(although they didn't normally stock it). You made a solution of it in a
plastic container and just dropped the crystal in and washed and checked the
crystal frequency at frequent periods to make sure you didn't overshoot. The
plastic container was kept on the shack windowsill and the fumes from it
caused the lower pane of the window to frost over!
Nevertheless, I found the most dangerious item around a shack is a high
voltage power supply (and the high voltage at the top of an LF loading
coil), and it is impossible to apply  H & S legislation to that.

Peter, G3LDO