Aqueous Deacidification - with Calcium or with Magnesium?
| Hlavný autor: | |
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| Médium: | Článok |
| Jazyk: | angličtina slovenčina |
| ISSN: | ISSN 0034-5806 |
| On-line prístup: | http://www.viks.sk/chk/res_1_98_1_40.doc |
| Abstrakt: | Summaries. In order to check the validity of the arguments recently presented against aqueous deacidification using Mg(HCO3)2 four old papers representing the types "brittle groundwood", "quality ground-wood", "chemical pulp" and "rag", and three types of laboratory handsheets (chemical pulp, cotton and unbleached linters, as used in the reporting institute for leafcasting together with deacidification) have been submitted to different aqueous treatments or production methods resp.: Ca(HCO3)2 and Mg(HCO3)2 solution, demineralized and tap water. Because in the previous reports contrary behaviour of relevant samples during dry and during moist accelerated ageing has been emphasized, the samples have been submitted to both methods of accelerated ageing and then checked for mechanical strength, colour change, pH, DP and mineral content. The evaluation of the widely diverse results is bringing about four main conclusions: ˙ there is no clear superiority of one aqueous deacidification method using earth alkaline carbonate ˙ conservation research should take into account the situation of practical conservation work and avoid overinterpreting chemical details ˙ an urgent need of conservation research would be a method of accelerated ageing imitating natural changes more closely than the methods usual at this time. Conclusions. 6.7 How to Deacidify From this last finding it can clearly be concluded that with chemical pulp paper any wet treatment improves the ageing behaviour, and that if the water used for that treatment is containing earth alkaline carbonate, the positive effect is enhanced. Possibly this well known platitude is the only valid statement regarding wet treatment and deacidification that can be given without restriction and further reasoning. If we disregard colour change, it can be extended to groundwood paper, while rag paper, slightly acidic, but strong, even if some hundred years old, does not necessarily and under all circumstances benefit from earth alkaline wet treatment: a bath in Mg(HCO3)2 containing water is reducing its mechanical strength, while Ca(HCO3)2 seems to result in slightly reduced ageing stability of this parameter. From the mechanical strength numbers achieved with laboratory handsheets a generally slight superiority of Ca can be concluded; it does not prove true with the real old papers. Yellowing and also brightness numbers are giving a clear superiority of Ca, which is reduced, but not contradicted by the real old papers. Altogether, these results were the reason for a change in the Institute where the experiment was done. In this Institute, the deacidification solution is prepared by further enriching the very good and hard tap water with earth alkaline carbonate under pressure of carbon dioxide8, and this solution is widely used, routinely, e.g., in the leafcasting machine. Following the results of the experiment the enriching procedure was changed from Mg to Ca. If it is true that the amount of buffer substance brought into the paper by deacidification is of less impor tance16, then this is a good decision. After a year or two it will be re-evaluated on the basis of experience in daily conservation practice. 6.2. Further Research 6.2.1. |
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| ISSN: | ISSN 0034-5806 |
