I am looking for a finish to apply to brass so it will not tarnish, but the finish must be acid free. Because the brass pieces will be used with archival pictures and documents, the finish can in no way compromise the archival process. I would appreciate any advice you can offer. K.S.
As I normally say, "I don't like to give advice, but if I were you, I would paint it." Owing to the fact that I am an organic chemist, I would suggest application of an organic coating as an acid-free, tarnish-free finish for brass. Such a finish can be applied as a conventional, waterborne, electrophoretic or powder coating.
Specific recommendations are difficult to make without a thorough review of the archival storage parameters. If the pictures were to be hermetically sealed in an environment excluding oxygen and moisture, the brass would not tarnish, since tarnish is actually corrosion caused by the action of oxygen on the brass surface in the presence of moisture. If they are instead stored in a temperature and humidity controlled room, they would already be exposed to painted surfaces, such as walls, floors, woodwork, etc. My point is that the nature of the aforementioned clear coatings for brass would be the same as those used on other objects in the storage environment.
Again, I don't like to give advice, but if I were you, I would contact suppliers of clear coatings for brass and have them tell you what materials (solvents, monomers, plasticizers, etc.) they would expect to be emitted by their coating in your storage environment. Suppliers of these coatings are listed on the Suppliers page or under the general heading Coatings on pages 408-411 and Paint on pages 482-483 in the 2001 Products Finishing Directory and Technology Guide.