Phytate: a Potential Conservation Agent for the Treatment of Ink Corrosion Caused by Irongall Inks
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| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0034-5806 |
| Online Access: | http://www.viks.sk/chk/res_3_95_143_160.doc |
| Abstract: | Conclusions. Most ancient irongall inks contain too much iron, partly present as iron (II) ions. These iron (II) ions catalyze the oxidation of cellulose by producing hydroxyl radicals from hydrogen peroxide (the Fenton reaction). This oxidation can lead to a loss of mechanical strength of the paper: ink corrosion. Ink corrosion can also be caused by the acid present in the ink, leading to acid hydrolysis. Changes in relative humidity during storage cause the iron (II) ions to diffuse out of the ink regions. By air-oxidation iron (III) hydroxides are formed, which are visible as brown ink bleedings, characteristic of ink corrosion. Ink corrosion is accelerated by a cycling relative humidity. Treatment of endangered paper samples with an aqueous solution of the complexing agent phytate leads to a remarkable protection of the paper against ink corrosion. In the iron (II)-phytate complex the coordinating position for hydrogen peroxide is blocked by phytate, and therefore the Fenton reaction is inhibited. No discoloration of the ink was observed upon treatment with an aqueous solution of sodium phytate. Therefore, salts of phytic acid are promising agents for the conservation treatment of ink corrosion on paper manuscripts and pen drawings. Further research will focus on the eventual adverse effects of phytate on brown iron oxyhydroxide-containing inks, the prevention of the brown stains by changing the phytate salt, the development of a nonaqueous treatment with phytate and the comparison of the effects of a phytate treatment with those of other agents, such as ammonium caseinate. The latter has also been shown to provide protection of paper against ink corrosion, possibly based on complexation of iron ions. Summaries. Ink corrosion, the degradation of paper by irongall inks, destroys paper manuscripts and pen drawings. The degradation can be attributed to both acid hydrolysis and iron (II)-catalyzed oxidation of cellulose. Phytic acid, a natural antioxidant, blocks the latter process. Its action has been investigated by simulating ink corrosion with accelerated aging tests at 90°C and a relative humidity, cycling each 3 hours between 35% and 80%. Mechanical strength was tested with a bursting tester at screen patterns, made with an irongall ink of a composition representative of old ink recipes. When ink corrosion occurred, the aged paper samples burst at the patterns. By deacidification with an aqueous solution of magnesium bicarbonate, the half-life of the bursting strength increased from 6 to 15 days. In combination with a treatment with an aqueous solution of sodium phytate, the half-life increased to 23 days. Surface pH values of both treated sets were similar. Therefore, the increase in stability must be due to the antioxidant function of phytate. Further research should lead to practical phytate-based conservation treatments of manuscripts and pen drawings threatened by ink corrosion. |
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| ISSN: | ISSN 0034-5806 |
