Mirror, Mirror On The Wall

           

Am I like other women? I maintain a mental map of where all the best mirrors are in my local town and studiously seek out the best ones to patronize when on my various shopping trips. You might think the best one is in the local upmarket hotel, but it is not.  It’s in the rather dated restroom of a 1960s public house with loud orange tiles. But boy does it have a good mirror. Properly positioned between two windows with frosted glass it casts a beautifully forgiving light. There’s a good landlady in charge, you can tell by the bars of fragrant rose soap. When I am there, I feel like a little girl who has been let sit at that site of thrilling alchemy, her mother’s dressing table, hoping that no-one will come in and break the spell. However, I always seem to have it to myself. That may of course have something to do with my sex, the time of day and the type of establishment I’ve guiltily sneaked into just to stand in front of that mirror!

Alas, just like the subjects they reflect, mirrors also age. Star-like constellations and concentric rings of grey, white and brown that resemble the wavy outlines of bracket fungus; while quite beautiful phenomena, their appearance on your antique mirror should come as a warning that all is not as it should be.  These are the visible manifestations of a long and inevitable process of deterioration that results from the inherently unstable nature of the majority of antique mirrors.  From the late Middle Ages until the mid-nineteenth century when silver came into use, the reflective backing applied to most mirror glass consisted of an amalgam of tin and mercury. Amalgam mirrors have a grey-blue tint, while silver mirrors have a yellow tint and will usually be painted on the back.

The amalgam layer consists of crystals of a tin-mercury compound suspended in a mercury-rich liquid.  The mercury is volatile and slowly evaporates into the surrounding air and mercury is of course poisonous. The mercury content of some mirrored boiserie (panelled rooms) left unopened for many years can reach dangerous levels.  As mercury evaporates, the tin-mercury  crystals become fewer and larger.  Eventually, small holes appear between the glass and the amalgam that glitter like stars. Liquid mercury has also moved by gravity to the bottom of the mirror so that it is very soft and vulnerable to damage from handling.  It is not uncommon to find drops of mercury that have accumulated on the mirror frame.  The fungus-like concentric rings appear in the advanced stages of deterioration where tin has reacted with oxygen in the atmosphere to form the rather charmingly named minerals cassiterite and romarchite.  The unfortunate news is that this is an irreversible process. There has been a practice in the past of turning such mirrors on their side so that the mercury might flow back over the rest of the mirror.  However, this is ill advised as it can flood the relatively stable ‘dry’ areas of the mirror. 

As a protective measure, it is best to keep the mirror in a dust-free environment.  Dust attracts moisture and is often acidic in nature.  Moisture and acidity accelerate the chemical processes of deterioration.  Fingers and spiders can also cause damage.  On some mirrors, it is possible to see the fine tracery of fingerprints and sticky spiders webs etched into the amalgam layer.  One method of protecting the amalgam layer from dust and spiders is to adhere a piece of paper or closely-woven textile over the entire back of the mirror, between the back-plate and the frame in such a way that it does not touch the actual mirror.  Silvered mirrors, if painted, may be cleaned with a soft pony hair brush and the dust vacuumed away. 

Please don’t be tempted to vacuum the amalgam layer on a tin-mercury mirror as mercury will be vaporized into the room.  If you wish to have the back of a tin-mercury mirror cleaned, it is advisable to seek the services of a professional conservator who will be able to deal with any hazardous substances.  They may also be able to ‘patch’ missing areas of amalgam to improve the mirror aesthetically should you desire.  Another option is to have the mirror ‘re-silvered’.  However, should you choose this option it must be remembered that this involves the loss of material original to the mirror.  Replacing the mirror entirely will also result in the loss of the idiosyncrasies of imperfectly formed antique glass.

Avoid commercial glass-cleaning products when cleaning the surface of a mirror as they contain substances which may accelerate deterioration.  It is best to brush the surface dust into a vacuum cleaner using a soft pony hair brush that is kept exclusively for cleaning mirrors in the house.  The glass surface may then be cleaned with 100% cotton balls dampened with lukewarm water to which only a couple of  drops of fragrance-free sensitive washing-up liquid has been added per litre.  Dry with a lint-free cotton cloth rolled into a loose ball so that the edges do not catch on the frame. If the mirror is in a gilt frame it is essential that no water is allowed to touch the gilding as it is very easily damaged.  Finally, mirrors of all types do not like extremes of heat or high humidity.  Avoid hanging them over fireplaces that are in use, against damp outside walls or on walls that receive long hours of direct sunlight.  Follow these few guidelines and you may enjoy your reflection for many years to come.

© Erica Devine     2011