I have one of these with the same pattern; some of you are using it as an avatar.
What chemical solution did you use to etch it?
I had a bit more success with ferric chloride (circuit board etchant) diluted with distilled water.
I used to get it at Radio Shack here in the states, but they are going, or have gone out of business.
I've always wondered if Stop Bath (used in B&W photography) would work; it's about the strongest solution of acetic acid that I know of.