Have you ever wondered what the word “gilding” means? It’s an ultra-sensitive and very beautiful decorative treatment that turns a surface into gold without actually creating something made of gold.
Gilding generally refers to the liquid gold applied through paint or other techniques to porcelain and other ceramics. The good news is that it looks lustrous and lovely when first applied. The bad news is that it shows wear when used frequently and is sensitive to its environment. In fact, after working with a recent client an O’Toole-Ewald appraiser found that it doesn't always require heavy usage to cause distress to gilding and that the saying that gold never tarnishes can be disproven.
About 20 years ago the client bought a beautiful bone china set decorated with extensive and intricate gilding. It had been placed in storage and when she recently retrieved it from the box in which it had been resting for two decades she found that the 24 carat gilding had taken on a red/black discoloration. Tarnishing film often looks red or black in appearance depending on what base metal is used, copper or silver respectively. However, it is extremely rare for high carats of gold to tarnish, so this case was at first a bit of a mystery.
While pure gold is not susceptible to tarnishing, almost all gold is mixed with some small percentage of other alloys, which can be vulnerable to tarnishing would only seen below 14 carats. In some cases 14 and 18 carats or even occasionally higher carats can tarnish, but it is extremely rare in gold as high as 24 carats.
If the base metals, in particular copper or silver, are exposed to corrosive agents, especially sulfur and oxygen compounds, tarnishing is entirely possible. Moisture, perspiration, perfumes, how you wash it, the water in which it is washed and even some foodstuffs can be responsible for the corrosion of gilding. But because the china in this case had never been used, it was unlikely that any of these were the culprits.
Through expertise, persistence and considerable in-depth research, OTE was able to determine the prolonged exposure to the organic sulfur containing compounds in the storage bags, in combination to the oxygen and sulfur in the atmosphere, had caused the gilding to discolor. The damage was determined to be inherent vice resulting from the chemical reaction of the gilding in its storage containers.
This case is a rarity. In India and the Middle East, especially, there have been more incidents of the tarnishing of higher carat gold, which appears to be a problem more specifically linked to the region. In Europe and North America tarnishing in higher carats of gold is much more unusual. In the past 30 years, there has been only one other instance, filed with the manufacturer of this china, of red and copper discoloration occurring on the gilding. Without the persistent research efforts of OTE appraisers combined with scientific sleuthing, this case may not have been solved.