| 配方类型： |
PAPER |
| 配方说明： |
Removing "Foxing" (Brown Stains) from Book Pages Stamps |
| 配制方法： |
The brown stain known as "foxing" sometimes found in old books, prints and postage stamps can be removed or made invisible by treatment with sodium hypochlorite. If the pigment used in the printing inks is affected by chlorine a milder treatment is to soak the affected stamp in a solution of potassium permanganate until it is stained brown all over.
The brown stain is then bleached out be treatment with dilute sulphurous acid. these treatments will bleach the discoloration due to the microorganism and also the natural darkening of the paper due to age or prolonged storage in tropical climates. The treatment is more satisfactory for used stamps than unused because the gum is necessarily removed in the process.
Although the discoloration caused by foxing can be bleached out, the paper of the affected part is generally tenderised by the action of the microorganism. Not all stamps can be treated in this way, because some old pigments are unstable to the chemicals used. Green and yellow stamps containing |
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