Each old book that you plan to deodorize has to be dealt with one at a time. Examine each book individually and try to identify the cause of the odour. Place books with damp pages in one pile and books with mould and mildew in another pile. All other books should be placed in a third pile.
You will need to do the most work on books with damp pages. Carefully sift through damp pages in the book and sprinkle cornstarch between consecutive damp pages. This may take longer than expected because sifting through damp pages can be a tedious job. When you are done starching one book, close it and set it aside in a dry place. Cornstarch will absorb excess moisture from the damp pages, considerably reducing the bad odour.
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After the books with damp pages have been left in a dry place for about 4 hours, take them out in the open sun. Carefully brush out the cornstarch that you sprinkled earlier and fan out the pages as evenly as possible. Prop up the books in such a way that they are supported by their covers. Leave the books in open sun for at least one full day if possible.
Now attend to the second pile in which you placed the books affected by mould and mildew. Remember that the chances of successfully salvaging books with mould and mildew and very rare. So discard the books that you think are not worth keeping. For other books affected by mould and mildew, you will have to contact an archival specialist for advice.
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Finally, attend to books that you placed in the third pile. On a bright sunny day, prop out the books in open sun. Leave them in the open sun for a full day. After every couple of hours, remember to fan out the pages in a different direction than before.