Kodak A-1671 manual Introduction, Methodology, Microscopic Blemishes, Molecular Sieves

Introduction

Microscopic Blemishes

Some processed silver gelatin microfilms in storage from two to twenty years have developed microscopically small colored spots or blemishes. The fogged leader at the outside of the roll is most frequently affected by the blemishes, which are generally red or yellow in color and are smaller in size than the image characters (for example, a typewritten letter reduced 20X) on the microfilm. The spot size does not increase, but the spots proliferate on the microfilm and can appear in image areas. A more detailed description of the blemishes and of the techniques used in inspecting microfilm is given in National Bureau of Standards Handbook 96.1

The spots are caused by local oxidation of imaged silver, resulting in the formation of minute deposits of yellow- or red-colored colloidal silver.2,3 Possible oxidizing agents entering from outside the roll of microfilm are aerial oxygen, whose action on the film is strongly accelerated by moisture, and atmospheric contaminants, such as hydrogen peroxide, ozone, sulfur dioxide, hydrogen sulfide, and nitrogen oxides, all occurring in industrial atmospheres. Assuming your microfilm was processed to established quality control standards, microscopic blemishes (redox) may still occur due to the oxidation of the metallic silver image, depending on storage or use conditions.

It is the opinion of image stability experts both within Eastman Kodak Company and outside of Kodak that the LE-500 designation for properly manufactured, processed, and stored silver gelatin microfilms is conservative and may be expected to outlive the designated Life Expectancy of 500 years. It is also, however, recognized that our world is changing. The increasing number of commercial solvents, auto exhausts, ammonia fumes, paint fumes, solvents, heating gases, and deteriorating cardboard and paper are only a few of the many sources of oxidants and peroxides affecting silver. These oxidants and peroxides are believed to be the cause of redox blemishes. Improper storage conditions also accelerate the formation of redox blemishes.

Once the deterioration of the microfilm occurs, it cannot be reversed. Silver film duplication, molecular sieves, and Kodak Brown Toner can be used to stabilize the microfilm and extend its useful life under varying storage and use conditions.

Methodology

Molecular Sieves

Molecular sieves, or desiccants, are chemical compounds that act as absorbers of water, hydrogen peroxide, and other oxidants. These sieves are also used to offset the vinegar syndrome caused by the decomposition of acetate film support4. The sieves are available in the following packet formats from a company called Multisorb, with the following part numbers:

Part #	Film	Format	Content
41 ag 43	16 mm	3.5 grams	400 (1 gal)
41 ag 47	35 mm	7.0 grams	200 (1 gal)
41 ag 51	105 mm	12.5 grams	125 (1 gal)

Rule of thumb: The sieve size is 2% of the weight of the roll of polyester-based film or 4% of acetate- based film.

It should be noted that the sieves need to be replaced at some interval, depending on storage conditions. The use of molecular sieves is cited by the American National Standards Institute (ANSI) as another procedure to reduce redox blemishes caused by high humidity conditions and oxidants in the air. For more information or to obtain molecular sieves, call Multisorb at 1-800-445-9890 and ask for Customer Service.

Kodak Brown Toner Treatment

Brown toning is a chemical treatment that changes the film’s processed silver to silver sulfide which is much more resistant to humidity and oxidants.

Kodak Brown Toner will not degrade the quality of the microfilmed image. After brown toning, areas of redox blemishes may be clear or change to a more neutral color. Although the name “brown toner” suggests a browner image after toning, this is not true for microfilm. In fact, after brown toning, areas of density may appear blacker or more neutral in color. Brown toning does not affect the D-min or clear areas of the film when washed properly.

The first documented evidence of redox blemishing occurred in the early 1960s. One recommendation from the resulting investigation promoted the use of low concentrations of potassium iodide in the fixing bath (0.2 - 0.5 grams per liter).3 This has been shown to provide a good degree of protection against redox blemishes. Kodak Microfilm and Prostar Fix solutions contain this stability-enhancing iodide. A second recommendation from this study was gold or selenium toning of the microfilm.

A-1671 December 2001 2