Hello Mike, I have etched all my stamps, and the smallest is 2 mm
with a monogram etched in it.
Use following like I do for file etching.
If it is going to fast (depends on the steel type and alloy
contends) dilute it op to 1/10 of the original formula.
You can see this that your etch ground (water resist felt pen, or
asphalt ground) is coming lose to soon.
This formula can also be used on files and burrs.
It etches more to the deep. than pure Nitric acid.
Clean the stamps, files in a hot washing soda bath with a brush, or
with an other way of decreasing.
Than put them in the following mixtuRe:
7 parts water
3 parts sulphuric acid
1 part Nitric acid.
In a few minutes ready. (Remember first water that acid)
Neutralize in washing soda again.