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[BKARTS] Alum tawed chemistry

Hi Nancy,

I've never experienced this because I haven't worked with alum-tawed
skins (other than as thongs) but I'm presuming it is a similar reaction
to the formation of iron gall inks. A metal ion, here I would think the
alum, reacts with the tannic acids (which would travel via the moisture
of the paste) to form a coloured indelible ink. Normally it would take a
little awhile to appear since the ink colour develops after exposure to
air. I wonder whether the spotting is related to the hair grain of the
skin? If the alum concentration was more in those areas or the moisture
wicked more into the follicles it would explain the 'peppering' effect
Jack mentioned. And the thinner areas of the corners would by default be
wetted more since there is less skin to absorb the moisture.  

The Ink Corrosion website is an interesting read -





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