“Now suppose you analyze the lead white from several paintings that you know were painted by that particular artist, and you find that there is silver, mercury, antimony, tin, and barium in every one of the samples. Also, each of these elements is always present in a certain concentration. Suppose also, that you have a painting which looks like it was painted by that particular artist but you’re not quite sure.
“Well, if you take a sample of lead white from that unknown painting and you find that the pattern of impurities is the same as in the paintings you knew were genuine, then the ‘fingerprints’ match. The chances of duplicating impurities of this kind by pure accident are extremely small, just about as small as the chances of finding two people with the same fingerprints. That’s why we call this a ‘fingerprint method’.”
“That sounds like a good idea,” said Harley. “Who thought it up?”
| x = one part per million (ppm) | |||||
|---|---|---|---|---|---|
| A known Rembrandt. | |||||
| x | |||||
| x | |||||
| x | x | x | |||
| x | x | x | x | ||
| x | x | x | x | ||
| x | x | x | x | x | |
| x | x | x | x | x | |
| x | x | x | x | x | x |
| silver | chromium | zinc | manganese | iron | cobalt |
| Unknown painting A | |||||
| x | |||||
| x | |||||
| x | x | ||||
| x | x | ||||
| x | x | x | |||
| x | x | x | x | ||
| x | x | x | x | ||
| x | x | x | x | x | |
| x | x | x | x | x | x |
| silver | chromium | zinc | manganese | iron | cobalt |
| Unknown painting B | |||||
| x | |||||
| x | |||||
| x | x | x | |||
| x | x | x | x | ||
| x | x | x | x | ||
| x | x | x | x | x | |
| x | x | x | x | x | |
| x | x | x | x | x | x |
| silver | chromium | zinc | manganese | iron | cobalt |
| Known forgery | |||||
| x | |||||
| x | |||||
| x | x | ||||
| x | x | ||||
| x | x | x | |||
| x | x | x | x | ||
| x | x | x | x | ||
| x | x | x | x | x | |
| x | x | x | x | x | x |
| silver | chromium | zinc | manganese | iron | cobalt |
Match the patterns of these lead white “fingerprints”. Unknown painting A is not a Rembrandt; it is by the same forger who painted the known forgery at the bottom. Unknown painting B is either by Rembrandt, one of his fellow citizens, or one of his students using the same paint.
“It was thought of many times by many people. But, it’s never been used for identifying paintings. In 1964 in the Netherlands, two scientists, named Houtman and Turkstra, analyzed about 40 different samples of lead white, 20 of which came from Dutch and Flemish paintings. The rest were samples of lead white not taken from paintings but obtained directly from the manufacturers. They analyzed these samples for different elements. These included silver, mercury, chromium, manganese, tin, antimony, and a couple of others.
“They found that the concentrations of these elements in the lead white from all the old Dutch and Flemish paintings were very similar. And the trace element concentrations were quite different in the modern lead white samples analyzed in the same way. At the time, they presumed that it was because the lead white in the paintings was manufactured so long ago. They may have been right to a certain extent.
“For example, they found that in all the old paintings there were from 10 to 30 parts per million of silver in the lead white, while in the modern samples of this pigment there were generally less than 10 parts per million of silver. All of them had been painted before the 19th century, and all the samples of pure lead white were manufactured during the latter part of the 19th century or during the 20th century. They believed that the reason the silver concentration was lower in the more modern material was because during the 19th century, lead refiners were doing a better job of removing all the valuable silver from lead.
Silver concentrations in lead white. The concentrations generally decreased after the middle 1800s. Notice also how the concentrations were very similar for all the older paintings (before 1700) which were Dutch or Flemish.