Saturday, 9 July 2011
1899 4c on 50c slate-purple and chalky blue
These are the common shades listed in the SG catalogue but the definitive text by Shipman and Cassels listed a lot more. Colour shades have several different causes. The printer may use a different ink; in the early days, inks were made up in batches as needed, and were rarely consistent. In such cases, the shade provides information about when the stamp was made, and possibly even identify a particular printing. Extreme variations may be considered colour errors. Inks may also be diluted or applied more thinly. It can also happen randomly, if a printing plate is accidentally under-inked.Ultraviolet light is destructive to a great many pigments, and can cause considerable lightening. In addition, some countries have used water-soluble materials known as fugitive inks to prevent reuse. Stamps of this type may be much lighter in color after being soaked.Some dramatic color variations occur as a result of chemical action; such stamps are called colour changelings. Forgers have also used chemicals to try to produce seeming rarities, although by now experts know how to identify these attempts.