Red, green, yellow and other colored chelated dyes are now used for various colored ballpoint inks.Pressurized ballpoint inks were developed about 1968.There are two types of fountain pen inks: (1) iron-gallotannate type and (2) aqueous solutions of synthetic dyes.
These inks are bright and attractive in color, but they are not nearly as stable as the carbon or blue-black inks.
Some of the synthetic dyes used fade and are soluble in water.
Carbon inks are insoluble in water, very stable and are not decomposed by air, light, heat, moisture or microbiological organisms.
This class of ink has been available for more than 2000 years.
In cases where known dated writings are not available for comparison with questioned inks, accelerated aging (heating the ink to induce aging of the ink) can sometimes be used to estimate the age of ink using any or all of the above described techniques.
Iron-based inks can be dated by measuring the migration of iron along the fibers of the paper by Scanning auger microscopy.
It is made into a liquid for writing by grinding the cake and suspending the particles in a water-glue medium. Liquid carbon inks are also commercially available.
In the liquid carbon inks shellac and borax are used in place of animal glue and a wetting agent is added to aid in the mixing of the shellac and carbon.
The dyes in ballpoint inks can consist of up to 50% of the total formulation.
Several other ingredients are usually added to the ink to impart specific characteristics.
Ballpoint inks made before about 1950 used oil-based solvents such as mineral oil, linseed oil, reci-noleic acid, methyl and ethyl esters of recinoleic acid, glycerin monoricinoleate, coconut fatty acids, sorbi-tal derivatives, and plasticizers such as tricresylpho-sphate.