| Abstract: | CONCLUSION. The pH variations obtained from different inks made with iron sulphate and gallic acid in variable ratios seem to indicate that the acid group of gallic acid contributes to the complex formation of the ink. As far as a saturated solution of iron sulphate is concerned, the ink will be darker and more dense as gallic acid increases. Similarly, we determined the pH of ink increases as gum arabie is added. SEM-EDX tests of ancient inks indicate the following conclusions. The Ca ratio in paper related to S and Fe in ink is very important in order to counteract acidity coming from sulphuric acid. Distribution and ratio of these three elements in the support changes according to ink acidity; therefore, in very acidic inks, the S from sulphuric is present in great amounts if we compare this element with Ca in areas around the ink. However, we do not find significant amounts of S in ink zones because S moves toward to the areas that border the ink, although we do find some iron in ink zones. Analysis of the organic compounds in the ink by GC-MS indicate the following conclusions: It seems that the fact that light inks are found is due to the scarce quantity of gallic acid used in ink preparation, as this acid could disappear with the passage of time. The dark colour of ink that bears no trace of acidity is due to gallic acid remaining in the ink. The fact that black colour is found in very acidic inks that carbonized the base is not because ink retains more gallic acid but because when the organic compounds and the base carbonize, black colour appears. It is the particular ratio of the three compounds gallic acid, iron sulphate, and gum arabie that determines ink quality and justifies its later acidic behaviour. |
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