As I’ve mentioned in previous collector posts here, here and here, it’s important to collect and archive any supporting documentation or content surrounding the original artworks you collect and house.
That means the bill of sale (documentation of purchase), certificate of authenticity and anything about that listing. I give a better explanation on Art Collecting Tip #1: Documentation.
But in addition to those things, it is a wonderful idea to collect anything else you can which would help identify the value of the artwork in the future:
1. Postcards, hand-written letters from the artist. Even email-correspondence with the artist that may be personal to you.
2. Art books or catalogs from the artist that is available either online or offline.
3. Advertisements or articles about the artist or their work. Even art show brochures/pamphlets that are sent out, mailed or posted could be valuable. You can create a history of their career in a way and show what it must have looked like, what work was shown there, etc.
4. Doodles, sketches, illustrations or rough drafts the artist may offer or discard. If you find articles like that around art shows or find them anywhere, keep those! Be sure you know that they are authentic or that they have the artist’s signature/writing somewhere to identify it’s authenticity. Sometimes I offer these things myself directly, so that collectors have a chance at the opportunity.
5. Photographs of the artist, in person, working, etc. You might have the chance to meet or see the artist in person. Whether they are attending a show, you run into them at a restaurant or event, there is a slight chance you could get a picture. Sometimes these are great supporting evidence of the artist’s career and life. They add value to their history as an artist. They add value to the art’s story. Try to find or procure your own photographs of the artists you follow and collect. You never know if these will be worth anything.