Polymathematica The Cleaning and Preservation of Metals - Treatment


Think small! This section relies upon you having the all-important Binocular Microscope through which small Hand Tools look huge. There really is no substitute for a binocular microscope to ensure control over the cleaning process. Starting with the premise that tool blades made from materials harder than your coin will scratch the surface, 'soft' tools for practice cleaning (on low value coins) should comprise:

  • Wooden cocktail sticks
  • Burnt matchsticks
  • Dried rose thorns/cactus spines
  • Dried spaghetti (!).
  • Initially use tools to lever upwards or sidewards the corrosion product and scale. The wood quickly blunts and often needs replacing. Spaghetti should be pushed, using its flat fractured end as a blade.

    However, as you come to realise that these are often next-to-useless for most applications, but come to value the precision removal capability they provide, you should next experiment with harder tools:

  • Silver rod (say 1 sq mm cross section)
  • Brass or copper rod (say 0.5 sq mm cross section)
  • Both the rods can be ground to give a blade by wiping across emery paper on a matchbox or similar. Make sure you wipe away any adherent abrasive before you start cleaning! Silver rod can be bought from a jeweller - it's cheap but check the price before you buy and you probably only need 5cm (2 inches) at most. Silver can be used for both silver and bronze coins. The brass or copper rod should be used for bronze coins only. In short lengths the two metals should be mounted in a pin-vice for ease of handling. It doesn't take too long before holding thin rod between the fingers causes a lot of discomfort. Again, initially lever the corrosion and scale material upwards, especially with the thin metal rods, pushing downwards can grind hard debris into the surface of the coins. However with care and practice, controlled downward pressure at the cliff face (as it looks under the binocular microscope) will cleave corrosion and scale from the metal - but don't keep pushing downwards, you'll pock-mark the metal surface.

    You will also find these tools inadequate for many applications. At this stage the hardest, and potentially most damaging tools, can be acquired and test-driven:

  • Steel needles
  • Hypodermic needles.
  • These should not be used in contact with metal surface, but be used to attack the deposits only. Under the binocular microscope, your first 'slip' will look horrendous. Pulling back in shock and fear and inspecting the coin with the naked eye will provide an opportunity to sigh with relief. The deep gouge at 40 x magnification revealing bright uncorroded metal will be no more than the finest of short scratches, barely the size of a gnat's ear.

    Finally, the tool to avoid is the glass bristle brush. Recommended by many for its rapid results, which can look spectacular to the naked eye, Polymathematica has contempt and disdain for this tail of satan. Not only does the glass scratch the field of the coin appallingly, the glass bristles end up over your desk (always), in your lungs and fingers (nearly always), in your eyes and occasionally elsewhere. Glass fibres really are awful contaminants in a domestic setting.

    On the subject of contaminants, although not yet rigged up in Polymathematica's laboratories, a small hand held vacuum cleaner could be of value. Much corrosion dust (containing inhalable metal) can be generated in a frenzy of coin cleaning. A vacuum cleaner, suitably adapted to suck through a thick straw, could be used to remove constantly the displaced debris. The only bag in which this rubbish should end up is the cleaner bag - not your lungs!

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    Last Update, 1-July-96