Volume 2, Number 3, Sept 1980, pp.1-2

Technical Exchange

A Comparison of Three Gaseous Fumigants:
Vikane, Ethylene Oxide and Methyl Bromide

I know of no publication that gives the pros and cons of the above three fumigants in their use in libraries, museums or other repositories.

All three of these gaseous fumigants are highly toxic to human beings and should be used only by professionals or trained personnel explicitly following the manufacturers instructions for their use. All federal and state E.P.A. regulations should be strictly adhered to, especially the post aeration. and testing for residual fumigants before the building and/or materials are used.

None of these fumigants leave a residual protection in the material or building, so that recontamination can occur almost immediately. Therefore care must be taken to prevent reinfestation by insects. By maintaining the proper temperature (68° F) and relative humidity (50% r.h.), the possibility of mold recurrence is minimized.

Vikane(r)

Vikane is the registered trademark of the Dow Chemical Company for sulfuryl fluoride (SO2F2). Vikane is a gas at room temperature. It is a professionally used gaseous insecticide. The building must be cleared of pets, plants, open food stuffs, etc., as well as humans. The building is then sealed by one of several methods e.g.: tenting, taping or caulking doors, windows, etc., which approaches an airtight building. The necessary quantity of Vikane (depending on the volume of the building) is "charged" into the sealed structure, and is allowed to stand static, for up to 24 hours.

The treated building is then aerated for the necessary time to remove all the Vikane before humans are allowed to re-enter. In the case of a home, the treatment usually takes 24 hours. For a larger building the time may be longer. Part of this time is in "set-up," sealing of the building, etc., aeration after treatment and testing. The actual soak time is about the same, approximately 16 to 24 hours.

Vikane kills insects such as ants, termites, silverfish, cockroaches, etc. There are no claims concerned with the use of Vikane for combating mold or microorganisms. At the present time there does not seem to be any method, report or recommended use of Vikane for chamber fumigation, such as is done with ethylene oxide.

Ethylene Oxide (ETO)

ETO is a gas at room temperature. It is used principally in vacuum chamber fumigation. The conditions and concentrations in the vacuum chamber can be varied so that the ETO will kill insects, larva and/or eggs, or combat mold and microorganisms.

Linde Division of the Union Carbide Corporation sells ETO in several concentrations. Most common are 90% carbon dioxide - 10% ETO (called Carboxide) or 88% Freon 12% ETO (called Oxyfume l2).

The material to be fumigated is placed in a vacuum chamber equipped for the use of ETO. The chamber is evacuated to 29.5 inches of mercury (0.5 inch pressure absolute, or 12 Torr). The ETO mixture is charged into the chamber until the vacuum is approximately 3 inches of mercury (26.5 inches pressure absolute or 675 Torr). These conditions can be varied depending on whether you are combating insects or mold. The "soak" time for insects is approximately 16 to 20 hours, for mold 5 to 7 days. This is the procedure used at the Library of Congress. These conditions can and do vary depending on the type of equipment being used.

It has been recommended that to "kill" mold the relative humidity inside the chamber should be between 35% and 55%. Certain chambers can accomplish this by injecting wet steam or water vapor into the chamber, but older systems do not have this capability.

Caution: In the fumigation of library materials, or museum artifacts, etc., the temperature inside the chamber should never be greater than 100° F. The kill ratio is for the above conditions and is not well documented for libraries. A 16 hour "soak" time for insects should give a 100% "kill" but some insect eggs may survive, especially if the relative humidity in the chamber is below 20%. (ETO does not leave any residual protection in the treated material and the material may be recontaminated before reshelving.)

A 5 to 7 day "soak" time for mold should give at least a 95% "kill." With low chamber humidity, mold spores may survive so that when the relative humidity gets above 65% the spores may become active, forming "fruiting bodies." (What equilibrium moisture on/in the book necessary for this growth to start is not known. This is a temperature/relative humidity relationship. When the temperature gets above 85° F and the relative humidity gets above 65% r.h., there is a very high probability of mold growth.)

ETO in a chamber should be used only by a trained person who, in most states, is required to have a license or certification for this purpose.

Methyl Bromide

The Dow Chemical Company and others manufacture this compound as a gaseous fumigant for insects.

The Library of Congress Preservation Office does not recommend the use of methyl bromide on library materials, especially leather, vellum, photographic films and prints. Methyl bromide appears to react with certain leathers giving off an obnoxious odor and also appears to lead to accelerated deterioration of these treated items. Methyl bromide should be used only by a professionally trained exterminator.

Technical information for Vikane and methyl bromide may be obtained by writing: The Dow Chemical Company, Dow Center, Midland, Michigan 48640, and for ethylene oxide by writing: Union Carbide Corporation, Linde Division, 270 Park Avenue, New York, New York 10017.

Parafilm M

Despite all the planned interaction that goes on at an AIC meeting, often it is the chance encounter that provides a solution for the conservation problem at hand. One such fortuitous encounter occurred at the Los Angeles County Museum of Art Conservation Center when a visiting objects conservator dropped in.

Prior to this visit, I had been puzzling over the best method of repairing the splits in two different ivory miniatures; one of which, a small oval, was split in half vertically, while the other, a larger rectangle, had several splits at the top and bottom edges. Both miniature portraits were delicately painted with water-soluble paints. Obviously, water-based poly (vinyl acetate) emulsion adhesives, such as Jade 403, could not safely be used to mend the splits.

I then proceeded to search the Art and Archaeology Technical Abstracts for articles on the conservation of miniatures. One article by Jim Murrell of the Victoria and Albert Museum appears in "Conservation and Restoration of Pictorial Art," edited by Norman Brommelle and Perry Smith. Mr. Murrell's method for mending splits involved the use of animal skin glue and mulberry tissue. The splits are first mended with bandages of mulberry tissue and animal glue, followed by overall backing with laminated rag board, again using animal glue for adhesive. A thin methacrylate film is applied to the paint around the splits prior to mending so that no stray moisture from the glue will damage the paint layer. This methacrylate moisture barrier no doubt is effective, but an element of risk is, nevertheless, inherent in this mending method since the chance always exists that the barrier may be imperfect. Also, removing the methacrylate barrier with acetone involves touching the very delicate painting surface with a cotton swab.

An alternative type of adhesive for mending the splits is wax, but even, overall application of wax to the ivory verso is difficult and complicates the process of backing the ivory.

Not fully satisfied with these possible solutions, I proceeded to clean the versos of the ivories and decided to ruminate over the ultimate solution to the splits.

At this point fortune, in the form of a visiting objects conservator from the East, intervened. Having noticed that I was dubiously pondering the ivories, the visitor mentioned Parafilm M, manufactured by the American Can Company, which he uses to mend split ivories. I asked about the film's stability. and he referred me to an article by Rustin Levenson and Marion Barclay entitled "Adhesives for the Strip Lining of Twentieth Century Paintings" from the 1976 Seminar at the National Gallery of Ottawa, Canada.

In the Levenson-Barclay article, Parafilm M is recommended as an adhesive for the strip lining of paintings. Apparently, the use of this material had first been suggested by Morton Bradley, a private conservator from Arlington, Massachusetts. Mr. Barclay had Joseph Tratnyek of Arthur D. Little, Inc. analyze Parafilm M. The film, Mr. Tratnyek reported, is composed of "innocuous polymers with adhesive and melt properties, and does not contain oil or plasticizers."

The working properties of Parafilm M are also briefly discussed in the Levenson-Barclay article. The film supposedly does not have a preferred orientation, but the side of the film that bears a release sheet is less sticky. This difference may be due to a releasing agent residue which is left on the Parafilm M when the release sheet is removed. The article also states that the film was activated by ten to fifteen seconds pressure with a tacking iron set at 40° Celsius when used for the strip lining of paintings.

Armed with this information, I decided to try laminating Parafilm M to a medium-weight Japanese tissue, and then heat-sealing a portion of the laminate to the ivory verso. I found that the Parafilm-tissue laminate stuck well to the ivory, conformed well to the panel contours, and was easily heat-released. Also, Parafilm M, under heat and light pressure, becomes more pliable so that the film edges flow and merge with the ivory back.

Satisfied with these test results, I mended the splits in both ivory panels with laminated Parafilm M - Japanese tissue bandages, blending the bandage edges into the panel. After the splits were mended, both panels were backed overall with one to three sheets of the film - tissue laminate for extra support. No rag board backing was necessary as the tissue support was decided to be sufficient, and the panels were to be housed in environmental chambers.

This treatment solution was most satisfactory. The properties of the material, Parafilm M, however, remain a concern as they are unknown. If the reader has any more information regarding this material, please write me c/o The Conservation Center, Los Angeles County Museum of Art, 505 Wilshire Blvd., Los Angeles, CA 90036.

The Question of Alum

A recent survey of all museum and mat boards used by the picture framing industry revealed that all but one of the boards contain ALUM. This survey was conducted by an industrial lab, who tested all products for alum and only one was found not to use alum in any of their archival products. Most paper products being sold today as "neutral pH" do, in fact, contain alum. Most manufacturers have neutralized the pH of the paper by washing a caustic (alkaline) solution into the paper during its manufacture on the paper machine. This raises the pH to 7, or over; but the sulfate radical in alum is never eliminated, and the acid reaction is still active.

Thus, the acid in paper is hidden...at least for now.