Normally these patterns are hidden, but chemical treatment can bring them to light. Cantu, many ink manufacturers started adding trace elements to their products in the early 1970's, changing the element each year in concert with each other. Cantu, whose laboratory helps Federal investigators detect such practices as the backdating of documents, said these elements make the dating of ink easy. Other chemicals that reveal age are the resins, starches and binders that help hold paper together.
In addition, more and more manufacturers are putting special clues into watermarks, according to Dr. Some papers have a tiny line under certain letters in a watermark that moves from year to year - revealing the age of the paper.
Even when examination of a piece of paper reveals no clear clues, age can often be determined because of the great strides made in analytical chemistry, Dr. One case involved a document from the Watergate investigations.
Congressional investigators suspected it had been written much later than indicated. Cantu went to the paper manufacturer but found the watermark and formula had not changed in the past decade.
IDENTIFYING the age of ink and paper - and thus tracking down forgeries as was apparently done in the case of the purported diaries of Hitler - is an art that has come of age in recent years because of sophisticated new techniques that can detect subtle changes in formulas, according to forensic scientists in and out of government.
Moreover, makers of ink and paper are starting to lace products with special clues as to when they were manufactured in order to help Federal investigators fight the rising tide of forgeries.
Before the 1960's, handwriting analysis and typewriter identification were the main ways to detect a forged document.
But today sensitive techniques such as thin-layer chromatography, neutron activation analysis and X-ray fluorescence help chemists in tracking down a forgery.
''Ink chemists get standards from all the manufactures and establish ink libraries,'' said Dr. Shaneyfeld, a private document analyst who worked for the Federal Bureau of Investigation for 34 years.
''They then punch out little sections of a line from a document under investigation, put it into solution and run it through the equipment.'' The comparison of known ink formulas that have changed over the years against a sample under study can help reveal its true age.
Clues in Decay of Ink The physical decay of ink can also be a clue, according to Antonio A. I.'' Simple techniques often suffice in the dating of paper.
Cantu, a forensic chemist at the Federal Treasury Department whose laboratory has the largest collection of ink samples in the world. In addition, electrically charged atoms or ''ions'' in ink will migrate into paper over time. If documents glow under an ultraviolet light, there is a good chance they contain optical brighteners - chemicals not introduced by paper manufacturers until the 1950's.