Good Morning everyone my aim here is to pass on what I have both been told, observed and discovered for myself in relation to the above. Although I do digress a little bit here and there lol.
Coins and artifacts made from good quality silver after a while often attract a black, blue grey or even pinkish colored deposit of oxides. What actions you take do depend on the condition. For good quality preserved objects I recommend the traditionally well-known use of water and tin foil rubbing to remove the oxides. (Where due to shape this is impractical then an established cleaner like “Silvo” etc. will suffice.) Rubbing with foil. This sure will make your house stink of Hydrogen Sulfide (rotten eggs) though. However one has to be careful here as over vigorous rubbing can sometimes give the object a “soft warm” appearance and cause detail to not be so obvious. Lettering for example can be enhanced by leaving just a trace of the darker oxide around it to make it more legible. Silver is rarely pure and is more often found naturally or deliberately alloyed with lead and other base metals. Impurities such as when alloyed with copper can result in greenish scabs appearing. (Yes Henry V111 you and your bloomin Groats etc. have a lot to answer for LOL.) In the past I have gently lifted these scabs with a modelling knife and successfully scraped them away, good eye sight required though. If the item is largely covered in adherent cladding of gritty green particulate then application of harsher chemicals can be applied if you just want to identify what it is i.e. a coin you have found and can see that its condition is poor anyway and of no real value. Some of the Antoninianus type coins of Roman period are base silver or copper core with a higher silver content wash. These are tricky and I would suggest a toothbrush and warm water only. Application of acids will cause your silver wash to migrate at a rapid rate leaving just a dull pink or grey core. If you prefer to just clean your silver coins and leave them in pretty much in an “as found” condition please note that moisture in the air in your house and repeated handling will turn them darker and lead to corrosion as the years pass. So they will require some sort of conservation treatment even if you just prefer to only lightly clean them in the first place.
This metal as we all know was and is widely used from sealing Roman roof nails to making artifacts, even coins to modern day roof flashing. Dependent on soil type it can be found in a pretty natural silver or glossy grey looking color, which could also mean it’s a “modernish” loss too. Alternatively some of its associated oxides can be black, grey, red, pink or even bright mauve in color. As it ages it normally become brittle and can illustrate crystalline appearing cracks and areas of separation. I recommend using a tooth brush and warm water again. A good long soak will remove most soil and loose corrosion deposits trapped in folds or designs such as on medieval period Vessica Seals etc. Lead and its oxides are poisonous and OK in the amount you probably have lying around are pretty harmless. However I treat mine as covered below in CONSERVATION section. Which protects them and of course you.
COPPER AND ITS ALLOYS.
Also dependent on the soil type in the area of loss such metals can appear pretty much as on the day they were lost. I've seen Bronze Age axe-heads come up that are still bright golden in color with only small areas and patches of green patina and minimal Verdi Gris. These still required treating to sort out the Verdi Gris and halt the onset of further oxidization to retain their as found coloration. Copper alone tends to go light blue green with age and also increases in brittleness often creating crystalline type cracks. Pinkish granular surface deposits are from the corrosion product called Cuprite. Brass and Bronze are the real issues for most detectorists in terms of preservation problems. Once again both can be as good as the day lost when unearthed, but more often than not they exhibit signs to some degree of patination or corrosion. Patina can vary from a light blue, to light green, dark green right through to brown and almost black. It’s worth noting that as a rule patination color is not always an accurate indicator of any great age either. I've seen the same glossy hard green patina found on good quality ancient coins also feature on the far more recent coins of Queen Victoria. When first starting I had some wonderful glossy light green colored pieces of fluted bronze. I was convinced this that they were fragments from some long discarded Bronze Age tool until someone declared they actually originated from a 19th Century Barrel Tap!!! A high tin content in bronze renders the alloyed metal very hard but also on occasion brittle as in Roman mirrors but means that it blisters and flakes under certain conditions with reddish scabby surrounded craters of green powder. These can be gently flaked away with a modelling knife and leveled but the damage they cause is irreparable. This type of corrosion is normally referred to as Oyster Shell Corrosion and is almost always associated with Bronze Disease. For objects that are really cratered with Bronze Disease I use a tiny abrasive modeler's drill bit in extreme cases and very gently “chase out” the craters by hand until they are clear of the majority of flaking powder. For tiny scabs of corrosion on coins in the past I have used a mix of water and cigarette ash into a paste and gently cleaned with a cotton bud, but any abrasive cleaning of a coin, must be centered on removing the corrosion deposit only, otherwise if applied to surrounding areas looking under a magnifying glass will reveal thousands of “Skater scratches” on the surface. The fag ash technique combined with a soda based toothpaste is also good for enhancing gilded objects by removing any calcareous lime scale deposits A toothbrush ironically is best for frequently removing the detached crud deposits and any excess agent that gets stuck in the design etc. Ancient copper / bronze coins particularly Roman issues sometimes attract a grey slate like substance that builds up and attaches as crud to their surface. Sometimes your find looks only worthy for the crap bucket. But underneath can be trapped a beautiful conditioned coin. Strangely this grey crud is the only thing I have used serious chemical warfare to defeat. Sadly it’s resilient to most, but the very harshest. Which soon demolish the crud and pretty you’re your coin to. The only real way to beat this I have found is the very delicate shaving of it with a modeler's knife until kit gets to a stage whereby a stiff toothbrush can polish off the remains, frequent clearing of the fine scraped away deposits is required so that you can see what you are doing and don’t suddenly clean down to shiny base metal by accident.
Only for Newbies and Beginners. That hard smooth glossy coloration on your finds is referred to as the Patina and it is this that is desired to be retained, protected and enhanced, never attempt to remove it back to the original shiny bronze etc. surface.
IRON AND ITS EFFECTS ON OTHER METALS
Note some parts of UK have iron bearing clays. All metals apart from gold will be effected to some degree with at the minimum a chocolate colored patina with bright orange dusting, which can be very appealing. In the extreme copper or bronze coins will attract iron through some sort of electrolysis and may be found as a ball of conglomerate consisting or iron oxide and sometimes tiny quartzite pebbles around the coin or artifact. The coins in these nodules appear almost burnt and are from my experience rarely in good condition. Some larger Roman coins may be stained by iron oxide and these stains cannot be removed. On occasion silver coins will also be stained badly too and this coloration has penetrated into the coin. such should also not be subjected to any attempts to remove. Of course it’s not just iron bearing clays from which iron effects other metals. Examples being corroded Roman knife blades, Saxon brooch pins, any object resting near to a nail for a long period and say bronze objects buried in a deliberate deposit along with Iron objects. For very light Iron stains and accretion removal there are clearly stated chemical preparations for removing them available on the market. Of course you have to decide if the expense is worth it.
Now after all that waffle LOL. I know there are a wide range of chemicals out there available for treatments and conservation of our finds. I’m sure some are good to excellent in their effects. However my methods are pretty basic, but I have Roman Sestertii and silver coins in my collection from 20 years ago which look the same as they did back then and have not discolored or cracked or shed fragments. Once I have got an object no matter what it’s make up metal or metals is or are I treat as follows. Here I must ad that my method totally seals the item so you need to ensure it is moisture free before doing this. Sometimes with new finds if it’s recently rained outside or I haven’t had the heating on I place them for 5-10 minutes in the oven with door open just to remove any vestiges of moisture then I apply my process as quick as possible. Now before anyone asks these procedures and benefits are what I have encountered. It’s simple so it should work for everyone, and yes I have used Micro crystalline waxes and oils but have discovered that both only offer relatively short term protection or enhancement and require re-applications. Whereas my method does not. NOTE: - Warm to hot water and toothbrush use will remove Lacquer if desired at any later stage. I have heard it said that some collectors prefer non –lacquered objects, which is absolutely fine. However as a footnote I have sold and swapped hundreds of items all lacquered and not come across this opinion, and anyway it’s very easy to remedy as I state above. So once you have cleaned object to the desired state
(1) Laying object or coin on a sheet of old newspaper as this is superbly absorbent.
(2) Using a gloss (I prefer gloss) or matt car paint lacquer I hold aerosol about 9 inches away and give a 1-2 second burst. Turning object as required, when done I immediately tamp off all excess with the newspaper and examine the coating. If it requires a re-application I just repeat above until it’s totally covered. Normally these lacquers are dry in around a minute.
(3) SIMPLE AS THAT. THE ADVANTAGES I HAVE DISCOVERED.
(4) Colored enamels even those that have decayed are enhanced and protected by the thin absorbed film of plastic.
(5) You can handle objects as much as you like with no fear from fingertip sweat based acids corroding or discoloring.
(6) Silver coins and objects remain in the desired color etc.
(7) Brittle or thin copper sheet type things like Royal Farthings and Jettons are given extra strength
(8) Delicate Gold gilding is enhanced and protected from flaking away.
(9) Powdery flaking craters from Bronze Disease are set rock hard and further effects are eliminated and also scabby green crusty Verdi Gris is stopped from contaminating other coins and artifacts in your collection.
(10) Now how you store your collection is another subject linked to ongoing Conservation and Preservation that perhaps merits some examination by us all at a later date on this Forum. . I once knew a fellow detectorist who had a good collection of big Roman coins….first mistake is that he left them untreated….second mistake he stored them in plastic sleeves in a coin album….every time he turned the heavy pages the coins clacked against each other and apart from each pocket having traces of moisture in them they also soon had a deposit of flaked and chipped patina dust evident in each one too….. After 5 years the coins were ruined. They had survived in good condition for nearly two thousand years before this fool “liberated” them. I hope you have found this useful if admittedly a tad basic.