“This is so important, that everyone should know about this, so i have put this in here, as a cautionary note”
If coins are found in damp conditions [most of the coins / artefacts, metal detectorists, find fall into this category] even being stored in a damp environment, or were not completely dry, before being stored, they can get the dreaded bronze disease, all though most objects are found with a certain amount of this disease…
Bronze Disease can be spread to other Coins or Artefacts;
Bronze Disease is a blue or greenish, soft powdery substance, which begins in one area and spreads (sometimes no bigger than a pin head) over time the coin / artefact will disintegrate & be destroyed because the process of the disease releases tiny amounts of muriatic or hydrochloric acid, which attacks more areas of the diseased object as it decays…
Even if you manage to remove it, without treatment it will certainly re-appear after a while…
Treatment: Manually remove as much rot as you can and then place the coin or Artefact in distilled water for 10 to 30 days depending on the size of the afflicted area, changing the water daily.
Then you can place the coin for two hours in an oven at 200° C or 400° F although this may not be necessary (don’t forget that this will darken the coin). Then coat the coin in microcrystalline wax or an equivalent to seal the coin and prevent the rot, coming back straight away, this might need repeating in five or so years, or sometimes earlier (so keep an eye on the coin or artefact, to be able to keep on top of the rot) & if the coin / artefact is to be stored with other items it must be kept in a sealed container or capsulise;