Changes in color and iron ions of commercial iron gall inks after artificial aging

Iron gall inks consist of vitriols (sulphates of certain metals), gall nut extracts; and gum Arabic: after exposure to oxygen, dark-colored compounds of the inks are formed. As the complexity of the composition of iron gall inks renders documents susceptible to environmental influences, this causes the handwriting thereon to fade. These add technical difficulties to the protection of iron gall inks. Therefore, it is particularly important to understand the changes in the inks during the aging process. For this reason, iron gall ink-stained paper specimens were subject to an intense analytical program to investigate their chemical and physical modifications after aging (temperature/humidity, temperature, and ultraviolet light aging), commercial iron gall ink was used for this experiment, making the study more applicable. The changes of iron gall inks were evaluated using color variation, color density, absorbance, and X-ray photoelectron spectroscopy (XPS). All results indicate that the temperature, humidity, and UV are harmful to the inks in both physical and chemical terms. Physical damage is mainly the aging of the ink color lightening, color density decreases, of which the color of the samples treated with damp heat for 30 days undergoes the greatest change. The chemical change is represented by the ratio of the concentration of iron ions in different valence states, the amount of Fe 3+ in the untreated inks is much greater than that of Fe 2+ , and the amount of Fe 2+ exceeds that of Fe 3+ after exposure to different methods of aging. Experiments show that UV light causes the most severe damage to handwriting. The main manifestation thereof is color-fade and the paper surface ink part of the iron ion content changes, with the increase of aging time, the Fe 2+ content gradually increases. This experimental study of the changes produced by iron gall inks during aging can provide better technical support for the protection of the ink handwriting.