COMMENT FROM: Dr Peter Spencer Davies
A collector and authority on Antique British Pewter
Antique pewter of the seventeenth to nineteenth centuries
We have got used to thinking of antique pewter as having a mid-grey coloured surface. However when pewter was freshly made by the pewterer and put on sale, it was bright and silver-coloured. When it was in daily use, it was kept bright by daily cleaning and scouring
However if it is not cleaned, the metal reacts with the oxygen in the air to form a surface oxide. This is the same process as that which creates rust on iron, or tarnish on silver. The oxide which forms varies with the composition of the alloy which was used to make the pewter. Articles made from a low tin/high lead formulation have a very soft oxide which is easily removed. Alloys with a high tin content have a very hard oxide, and alloys with high antimony have an extremely hard oxide which is harder than the parent metal. Fortunately, the oxide forms slowly, so antique pewter collectors who like their pewter with a lustrous surface need only polish their pieces every five or ten years.
So antique pewter can vary in color from silver to medium grey to black, depending on how long it has been since it was last polished. Unfortunately, the oxidation is often not uniform, and there can be local patches, probably reflecting lack of uniformity in the composition of the underlying alloy. In some cases, the oxide burrows down into the metal and in plates and chargers it is not unusual to find that the oxide has eaten right through to the back.
This variation in colour presents a dilemma for the antique pewter collector. Should one collect only pieces which have not been cleaned for a hundred years or more and are therefore grey or black in colour? Or should one display antique pewter in the condition that it was in when it was in daily use? Most collectors who opt for the latter (and that includes myself) nevertheless prefer to see signs of antiquity on their pieces, as revealed by traces of the oxide in parts which would have escaped the polishing rag over generations of care.
So if you buy a piece of antique pewter in dark condition, unless you prefer it that way, you will be faced with cleaning it. A light oxide on a high lead composition measure can often be removed with a hard rub with a proprietary metal polish. Failing that, start off with a very fine (saya 600 grade abrasive paper). If you have a very dark heavily oxided piece made from hard metal, you are in for a long and dirty clean up process. It is often virtually impossible to remove hard oxide with abrasive (emery) paper. The oxide has to be softened and freed from the underlying metal. This can be done by soaking the piece in a strong solution (about 10%) of either hydrochloric acid or caustic soda. These are both extremely dangerous solutions and you should only undertake this if you have protective clothing and preferably some experience of working with these chemicals. Hydrochloric acid has the advantage that areas which you do not want to be attacked, such as the undersides, or the backs of thumb pieces etc. can be masked by a thick covering of Vaseline or similar grease. However any piece treated in this way should subsequently be subjected to several days of immersion in changes of tap water, to remove the last traces of corrosive chloride ions. Caustic soda solutions are very effective, but the caustic will attack and dissolve anything you try to mask with.
Following removal of the oxide, and many washes with tap water, the piece should be dried. The resulting surface will be dull and may well be pitted. The next stage therefore involves bringing back a smooth surface again, by successively rubbing with finer and finer grades of emery paper. The more heavily scarred and pitted the surface at the outset, the coarser the grit size you will need to start with. As you move to successively finer grades of emery you will be rubbing away the scratches left by the previous grade. Ultimately you will be able to finish off with a metal polish. It is a long and dirty process, but often it is the only way to bring back a piece which has been neglected and left to 'rust' for generations.