I have been experimenting with HP quite a
bit recently. Just the 3% stuff though.
I have only used it a room temperature though reading through old threads people seem divided over whether to warm it or not. If warmed some said to use a double boiler, other the microwave (warm it before you add coins). As I said I have only done it at room temperature.
As several others have said, it seems to
work well on most soils and even soften some lighter encrustations. I check the coins after about an hour and then after a few more hours. I have taken some out at the first or second check and left others in overnight. By morning the coins have stopped bubbling and I think the HP is now simply inert DW. It is very dirty and cloudy. I usually fill a small
bowl to about 1" depth and
work on 5-10 coins.
I have tried on coins that were in DW soaks for months. In some cases (maybe 1/4) the hard dirt that was not budging with the DW softened so I could
pop it off. In the rest of the cases no real effect yet. I have only placed these coins back into DW. I have not yet given any batch of coins multiple soakings in HP. Not sure if that would be too much for the
patina to take.
I have also done a few "initial soaks" with HP. I did a rinse in warm tap water then into the HP. This seemed to
work better than DW for an initial soak but certainly did not remove or soften all dirt. (And was way more expensive!)
I always soak in DW after soaking the coins in HP.
So far I see no signs of damage to the
patina or coins. That said I have not done this on any coins which clearly
had a very nice
patina showing through. Only on the "
average"
types one finds in Balkans etc.
I will keep experimenting but at this point I think HP might be a
good soak for coins with stubborn dirt after they have
had a few months of DW soaking.
Shawn