PittingMost people choose not to polish a piece, based on the amount of work involved. Modern environment friendly metal polishes reduce re -polishing to a minimum and thus the amount of work involved. 
Now that the shine lasts longer, all that is needed is a dust with a dry cloth or a wipe over with a damp cloth every so often. However not everybody is using environmental friendly products and years of polishing with incorrect products and techniques, can have serious effects on antique pieces. We cannot emphasis enough the importance of using the correct metal polish and metal polishing techniques.
Our video Polishing Metal Antiques gives a step by step approach to polishing these coveted and much cherished items. By following the advice in the video, you will keep your antiques in good condition for many years to come. However over polishing is something different altogether.
So many antiques have been ruined by over polishing or polishing with the incorrect polish. It still amazes us that people will spend money on purchasing an antique, but will not purchase a quality polish to keep it in good condition.
Over PolishThis lovely 1700's brass candlestick was saved from the scrap bin so that we can use it to illustrate the disastrous effect of over polishing and the use of incorrect polish.
Metal polish contains two basic ingredients, abrasives and a liquid cleaning component. The abrasives are required to remove the hard oxide layer on the metal surface, and the liquid component cleans the surface.
Most environment unfriendly metal polishes contain acid or ammonia as the liquid cleaning agent and hence are commonly referred to as anhydrous chemicals. Both acid and ammonia are bad for metal antiques for the following reasons.
Over Polish During the 1700's, the kitchen staff noticed that the copper cooking utensil became bright after making preserves, pickles, jams, marmalade and similar, all of which contain vinegar as a preserving agent. By mixing vinegar with ashes from the wood fires they produced an effective polish to shine the copper cooking utensils. Although the components in modern metal polishes are now commercially manufactured, the technology has not changed since the 1700's. The acid etches the surface of the metal making it rough. The more rough the surface the more dull the shine. When using these products without protection you can feel the acid attacking your skin and this is the same for the metal surface.
Over PolishAmmonia has been used to clean metal since around the 1700's or earlier. Metal polish was not manufactured in the 1700's so the butlers and servants made their own metal polish. In those days the horse was the basic means of transport and what they discovered was that horse urine could be used to clean brass items. The straw from the horse bedding was ground into a powder to form the abrasive component which, when combined with the ammonia made an effective metal polish. The ammonia from horse urine has been replaced by a commercially made product and the straw replaced by another component. Thus the 1700's product forms the basis of the majority of metal polishes used today. Since the 1700's, technology has developed such that humans have landed on the moon, so why has metal polish not changed significantly from the 1700´s. The answer is simple, money or more accurately profit.
Over PolishBoth acid and ammonia are relatively cheap components that speeds up the oxidation process, so the more you use these products, the more you have to use them. Good for the metal polish manufacturers profit but not so good for your wallet nor your antiques.
Brass is an alloy of copper and zinc and ammonia dissolves zinc. Look closely at old brass items and you will usually see small pit holes in the surface. This is known as pitting corrosion caused by a process called dezincification where the zinc has been dissolved leaving a hole, pit or crater. 
Also the abrasives used in modern metal polish are usually much too hard or incorrect for the surface being polished and will either scratch or wear the surface away. Cheap metal polishes usually contain harsh components that give a quick shine that does not last and causes long term damage. Where metal polish is concerned, you really get what you pay for.
Be kind to your antiques and use a modern environmental friendly polish, the caring way to a high lustre long lasting shine.