This explains the origin of the name blue-black fountain pen ink. This ink is insoluble in water and cannot be effectively erased by abrasion.
The most popular fountain pen ink (developed in the 1950s) consists of an aqueous solution of synthetic dyes.
Cartridges containing this ink are under the pressure of nitrogen or some other inert gas.
When dating tags are detected, it is possible to determine the actual year or years when the ink was manufactured.
Dating tags are unique chemicals that have been added to ball-point inks by some ink companies as a way to determine the year the ink was made.
Relative age comparison tests performed on inks of the same formula and written on the same type of paper with the same storage conditions (performed by measuring changing solubility properties of inks) can estimate how long inks have been written on paper.
This is done by: (1) comparing the rates and extents of extraction of questioned and known dated inks in organic solvents by thin-layer chromatography (TLC) densitometry; (2) comparing changes in dye concentrations by TLC and TLC densitometry; and (3) comparing the volatile ink components by gas chro-matography-mass spectrometry (GC-MS).
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The most modern inks of this type contain pigmented dyes, such as copper phthalocyanine (introduced in about 1953) which makes these inks much more permanent.