Faded Ink on Paper
Unfortunately, there is no way to restore faded ink to its original state. Some chemicals are advertised to darken original inks, but they are often damaging to paper and conservators do not recommend them.
The only way to make aged or light-struck media on paper more legible is to ask a conservator if it is possible to lighten the paper support. This would increase the contrast between the paper and ink. However, this process is not possible with all types of paper or inks.
If your primary concern is legibility, we recommend making a scan or high-contrast photocopy on a dark setting. If you do not have a photocopier or scanner, try taking a photo of the document and changing the contrast settings. Often this technique will help your eye distinguish text and lines more easily.
If the ink is legible, we still recommend making a digital copy of the letter or document because, as the ink fades further, it may eventually lose all legibility.
This letter’s ink has faded. Unfortunately, no amount of conservation could safely darken the ink to help with legibility.
This is the same letter. The letter was photographed and the contrast was increased. As you can see, the text is much easier to read.
See here for more information about reading documents with faded ink from the Smithsonian Institute Archives.
How to Prevent Ink From Fading
Light is the greatest enemy of ink. Not only is writing ink damaged by UV rays, but so are watercolor pigments, pastels, and drawing inks. Therefore, the best way to prevent the fading of ink is to store the document away from all UV exposure. You can find general information on how to care for your collection here.