These tend to result from long-term storage in sub-optimal conditions, which you'll encounter both in things you've stored yourself (if you're unlucky) and in items bought at car boot sales, flea markets, bric a bracs and so on.
Please note that I am NOT a trained restoration expert, and that we're totally not responsible for any damage that may result from attempts to reproduce these techniques. They're just what seem to be working for me so far. For similar reasons, I welcome feedback, comments, and suggestions based on your own experience.
|This stuff basically runs on witchcraft|
I started with a kilo, which I divided between two smallish plastic boxes that I'm using for this proof of concept. The one below contains two glossy-paper game manuals that smell of mildew but have no visible spores. They are otherwise clean and in good condition.
The next box, shown below, contained two books, one of them fairly rare but in terrible condition, that I rescued from a mouldering box of a friend's possessions during a storage clear-out. They're on standard paper, which is easier to deodorise and dry out than anything with a glossy finish, but which is also more prone to absorbing smells and moisture. In addition to being kept in an outdoor storage locker for years, they were previously exposed to cigarette smoke, various flats full of less than entirely house-trained cats, and sundry other environmental hazards, as well as simply being very well used in the course of things.
|Small items are buried in bicarbonate of soda and sealed into an air-tight box|
|Large items get much the same treatment, only in a storage tub|
Addendum: things that don't work
Crystal cat litter is made of silica (the same stuff that goes into those moisture-absorbing bags marked "do not eat" that come with every item of electronics you've ever bought). A technique frequently recommended for de-ickifying (technical term) paper is to take two plastic boxes, one larger than the other, place litter in the large box and the item in need of deodorising in the other, inside the bigger box, without a lid. You then place an airtight lid on the larger box. I can safely confirm at this point that this does not work in the slightest.
|Silica cat litter: doesn't work|
I also wouldn't be happy using cat litter for anything with particularly fragile paper, as the crystal chunks are a little on the hard and pointy side. The small amount of resulting dust was easy to clean off, at least - I'd definitely not try this (or even the box-within-a-box technique) with other kinds of litter, and I don't think that the technique provides any advantages over the bicarbonate of soda method detailed above.
In future instalments, we'll look at cleaning box exteriors, plastic items, and floppy disks.