pigment

However, why this pigment is there and what it might do was unknown.

Tattoo is just a decorative pigment on skin.

Say we determined a pigment was made with zinc, for example.

So, you can see why this type of analysis requires a knowledge of the history of pigments, right?

Then we compare these signatures with those of particular elements like zinc or lead, to determine what the pigment was made of.

And using ultraviolet light we can see the spectral signature of each component part of the pigment.

You've got to find out what's in those pigments, learn their composition, and that requires lab work - detective work really - in a word, Spectroscopy.

Since you're trying to verify if it’s a Rembrandt, the ingredients in the pigment would need to have been used during Rembrandt's lifetime - in the 17th century.

You'd have to know when he created his paintings, um... what pigments he used, in other words, what ingredients he used to make different colors of paint, ‘cause the ingredients used in paints and binding agents plus burnishes, finishes, what have you, have changed over time.

You are better off using a pure green pigment.

Like I said before, these pigments deteriorate rapidly so we really need to do the research before the traces are gone so that we can increase our understanding of ancient polychrome sculptures and the cultures which created them.

There are many, many more sculptures that have traces of pigments left on them and we have the technology these days to be able to carry out effective studies of these pigments.

And let's consider the extensive traces of a red pigment that were found on the statue's cloak.

The use of these pigments showed the importance of Augustus and that he should be honored.

They were from expensive pigments.

And it turns out that the colors weren't just from any pigments.

It's now generally accepted that most, maybe even all marble sculptures from that time period, receive some kind of surface treatment, like the application of pigments, colored stones or metals that would've modified their color.

In other cases, the pigment may have been weathered away while exposed to the elements or someone may have rigorously cleaned the statues and unknowingly removed the last traces of pigment. 

In many cases, the pigment would've simply deteriorated.

For example, if you look closely at a red leaf on a tree, you'll notice that most of the red pigment is on the upper side of the leaf, the side facing the sun.

It's a red pigment called anthocyanin.

Well, it's probably true for pigments like yellow or orange, but it doesn't seem to hold for the red pigment.

According to the classic theory, this is true for the red pigment as well.

As this happens, the other pigments present in the leaf become visible.

As a result, the French government sponsored a competition in 1824 to find a cheaper way to make ultramarine pigment.

The process was time-consuming, which also contributed to the high cost of producing ultramarine, and it didn't even yield much usable pigment.

Actually, the ancient Egyptians did manage to make an artificial blue, the first synthetic pigment in fact, if you can believe that.

And you even have the wealthy ordering paintings with ultramarine to show others that they could afford something made from this precious pigment, much in the same way they would order gold leaf.

So, blue, and especially ultramarine pigment, was a luxury, a status symbol, worth even more than gold at times.

For example, use pigment from lapis lazuli or azurite very sparingly, and also use something cheaper, like smalt, which was made of ground glass.