Science reveals biblical rainbow

Azurite, cinnabar, malachite, verdigris, carbon: These are the true colors of the Bible — the Gutenberg Bible, that is.

For the first time in 600 years, the world has become privy to the mysterious substances used to illustrate the rare volumes of God’s word produced by the German printer Johann Gutenberg circa 1454.

It took a pair of enterprising researchers with a delicate touch to isolate the composition of the nine colors — painstakingly concocted by unknown artists from such substances as precious metals and minerals, ground chalk, copper, plants and even insects.

Gregory Smith, an artifact conservation specialist at Buffalo State College in New York, and Robin Clark, a chemist with the University College of London, managed to collect tiny fragments of paint tucked in the inner margins of the King George III copy of the Gutenberg Bible at the British Library.

Using a process called Raman spectroscopy, the two sent a tiny laser beam into the paint bits and on a few selected pages of the Bible. By analyzing resultant characteristic light patterns, they identified the chemicals that enlivened decorative letters or intricate drawings of flora and fauna.

“What is surprising is that this core knowledge of pigment composition had not until now been established, bearing in mind the colossal amount of art historical research which has been carried out on Gutenberg Bibles over the past six centuries,” Mr. Clark said.

“Spectroscopic chemical analysis represents an important first step in an appropriate conservation and preservation strategy,” said Mr. Smith, who cringes at the idea of using inappropriate restorative preparations on such a book — which took the skins of 191 calves to produce back in its day.

The two researchers found that Gutenberg’s bright red is actually cinnabar, or mercuric sulfide. Yellow is lead tin yellow, — or lead stannate. Black is carbon possibly taken from lamp soot; blue is azurite, or copper carbonate. White is calcium carbonate, or chalk. Olive green is malachite, while dark green is verdigris, or copper ethanoate.

They struggled with gold and a lush, dark red, eventually concluding that the former is gold metal and the latter an organic pigment possibly gleaned from insect bodies.

Gutenberg originally printed 180 of the Bibles, using a Latin translation made in A.D. 380 of the Hebrew Old Testament and the Greek New Testament. The volumes — some fancier than others — brought the text to the public for the first time. Forty-eight copies of the Bibles remain.

The researchers’ revelations now provide a road map of sorts to those tasked with preserving and protecting the remaining volumes. The pair has discovered the presence of modern chemical compounds in Bibles located elsewhere in Europe, indicating misguided attempts to restore them.

“If you don’t know the chemical composition of an artifact, such as a manuscript, you have the potential to damage it by using the wrong chemicals,” Mr. Smith said.

The research will be published June 1 in Analytical Chemistry, a journal published by the American Chemical Society.