I'm with Lino on this. HCl by itself doesn't dissolve copper but it can do it in a roundabout way.
1. Oxygen slowly oxidize the surface of copper and HCl can dissolve copper oxide creating copper chloride (CuCl or CuCl
2). Going on to step 2 or 3.
2. Copper II chloride (CuCl
2) easily dissolves copper creating copper I chloride (CuCl).
3. Hydrochloric acid with the help of oxygen transforms CuCl back into CuCl
2. Go back to step 2.
Each cycle 2 -> 3 doubles the amount of copper II chloride that actually does the dissolving of copper. This is the process that we are trying to call copper chloride etch but most people wrongly calls it AP from acid peroxide.
A deeper understanding of what goes on in our beakers only makes it easier to control it and correct problems when you is facing one.
WARNING!!!
Do NOT, I repeat do NOT add hydrogen peroxide to a beaker with metallic silver. It can be in best case wasteful or in worst case cause a steam explosion or a serious boil over.
Silver decomposes hydrogen peroxide into water (steam) and oxygen and is used to fuel rockets!
The large surface area of cemented silver would instantly decompose even weak peroxide into oxygen bubbles and hot water.
If you take a piece of clean shiny copper and boil it in a flask with a reflux condenser (or in a beaker with a watch glass lid) virtually nothing happens, but if you take out that piece, let it sit in air a couple of days to get a decent oxide coating and then toss it in a shallow beaker with some cold HCl and put it outside for a few days and the copper will dissolve. This is from the oxygen n the air diffusing down into the HCl and working it's magic. You could actually see how far the oxygen gets in a beaker without a bubbler, there is a clear difference in color between the oxygen starved layer with dark brown CuCl and the oxygenated layer of emerald green CuCl
2
But just as Lino said in so much fewer words, HCl needs the help of an oxidizer to dissolve copper.
Brown copper chloride, both in solution and precipitated as white crystals from a saturated solution.
Green copper II chloride, both in solution and as needle-like crystals.
Göran