Paper, especially inexpensive paper like newsprint, deteriorates over time, becoming yellow and brittle. This has to do with the acid and lignon content of the paper. The Library of Congress has a summary of the issues involved.

If you have paper you want to preserve, such as newspaper clippings, a paper ketubah, or other old documents prone to yellowing, there is something you can do which will significantly increase the longevity of the paper.

Originally developed for preserving books and paper documents in libraries and archives, several companies now produce spray bottles that you can use to de-acidify paper. The sprays soak into the paper and then quickly evaporate, leaving behind an alkaline buffer that helps prevent any further deterioration of the paper.

One company, Preservation Technologies, makes two brands of de-acidification sprays, Bookkeeper and Archival Mist. Bookkeeper is their original product intended for use by professionals in libraries and archives. Archival Mist is their consumer product, which is sold in smaller quantities. It’s not clear if there is any difference between the two products other than the branding and the size of the spray can. If you’re planning on spraying a lot of documents, you might find it cheaper to buy the Bookkeeper product line, which comes in larger quantities. Bookkeeper is available from the big archival product companies like Light Impressions and Print File in various sizes, while Archival Mist is available more broadly, in craft stores, etc. Overstock is selling Archival Mist for $14 and Amazon has it for $17.

Another company called Provenance has a de-acidification spray called PaperSaver. PaperSaver is sold in both aerosol cans and in bulk.

University Products sell all three products.

Any of the above products should work similarly. Just spray both sides of the piece of paper and after a couple of minutes the paper should be dry and non-acidic. Now store the paper documents in a non-acidic storage medium and keep it away from heat and humidity.