I do a lot of etching in silver. Firstly, you need to be aware that anything that etches metal is going to be a relatively dangerous chemical, although you can go for chemicals that are less dangerous than others.
To etch silver most people use nitric acid which works very well and quickly. However, I work from home and do my etching in my kitchen and I just don`t want to have proper acid here.
So I use ferric nitrate instead. This works well, but it`s much slower than nitric acid. It also has a tendency to badly stain some surfaces - and usually the stains don`t show up until days later - so you need to work very carefully with it, always use gloves (your fingernails will go black otherwise!) and clean up meticulously if there are any splashes.
If you want to etch copper you can use ferric chloride, which is much easier to get as a lot of electronics people use it to etch circuit boards - if you go to an electronics shop chances are they`ll have it. People will tell you that it etches silver ... but unless you have weeks to wait to find out if it works, I wouldn`t even try. The best result I`ve had after hours and hours is a very faint shadow on the metal.
Hope that`s a start!
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