Silverlocks

The red spots are gold oxide formed through (I think) electrolytic reactions involving impurities on the surface of the gold. They decompose at 160°C. If you hunt around on the interwebs you can see videos showing you how to gently heat a coin up with a blowtorch and get rid of them. I did try this with a sov that had a red spot and it does work. Just don't overheat the coin. I used a butane torch of the sort you can buy off Amazon for melting the sugar on creme brulee (should cost about £20 including a few cans of butane), and a jeweller's charcoal soldering block to put the coin on; you can get these off ebay for about 10 quid.

Next time I get a really grubby sov in I'll take some before and after shots.

Not to mention that the coin itself is in really good nick. Jubilee Vic effigies wear terribly.

I just bought some ammonia from a chemical supply place. The bottle I got was really a bit too strong so I dilute it down with maybe 2-3ml ammonia to 10ml distilled water and that works fine. It won't react with gold or silver - really the only strike against it is that the concentrated solution is very smelly.

If you've got a nice shiny new coin you can get a film of gunge left as it evaporates off. Rinsing the coin in distilled water and leaving it to dry on a clean cloth or some such mitigates this at the expense of it taking longer to dry. You can get 5l bottles of distilled water off ebay for a few quid.

Pretty much everything I've bought I got through Ebay. They won't ship some stuff - you can buy 32% hydrochloric acid (cleans lime-based mortar stains off brickwork) from Homebase but nobody will ship that from Ebay. Some chemicals (e.g. Nitric acid) are subject to legal restrictions as precursors to manufacturing things like explosives or narcotics, and you can't get those without a licence, but a pretty wide variety of chemicals are available on the open market and can be ordered and shipped. In theory, you could do precious metal recovery with chemicals that can be obtained without a licence and mostly purchased online. Given the fumes, you might not want to try that in a council flat, though.

Vendors on Ebay will ship most chemicals that aren't subject to legal restrictions. If they're dangerous they will come packed in a plastic bag full of activated charcoal.

I've tried a few solvents, notably: Acetone - dissolves most grease based gunge. It's also miscable with water so you can rinse coins in distilled water if desired. Isopropyl Alcohol - Acetone is better, IMO, but this works. Limonene - This is degreasing agent widely used in cleaning electronics. It's the orange smelling stuff you use to clean heatsink gunk off CPUs, for those familiar with it. It works, but it's very, very smelly and has no discernible advantages over acetone. Ammonia solution - Probably the strongest cleaning agent for grease based stains; you can rinse coins off with distilled water. It won't react with silver or gold, but it will form cuprammonium complexes from copper salts. I've never tried it with copper coins. I got a little borosilicate petri dish and lid off Ebay. This lets you immerse a coin with about 10ml of solvent and pop the lid on it (good for anything that produces fumes). I also got a 10ml pipette for transfering solvents into the dish. Usually soaking in acetone and/or ammonia solution for a few minutes is enough to dislodge most gunge and bring the coin up nicely. One thing I did consider is getting a water pik toothbrush for rinsing and using distilled water for the rinse.

That dates you. I'm no spring chicken and there are quite a few folks on this board who are substantially older than I am. Folks who remember the 1960s, which apparently means that you didn't really participate in them.

Original - he's quite old and semi-retired now.

The distribution isn't skewed as far as I'm aware.

I wondered about that - Lawrence Chard is fairly active on social media these days, which is where I heard of Chards from. You can see him pop up in The Silver Forum from time to time and they put out a bit of content on YT.

Is that the same outfit as Chards?

There's a saying that goes: Think how dumb the average person is. Now, remember, half the people are dumber than that.

As a general rule of thumb, rate of reaction doubles for about every 10°C temperature.