I read the Summer 2003 article “BEVA 371 and Its Use as an Adhesive for Skin and Leather Repairs: Background and a Review of Treatments” by Lisa Kronthal, Judith Levinson, Carole Dignard, Esther Chao, and Jane Down (JAIC 42[2]:341-62) with the greatest of interest. It is a thorough, meticulous report on the use of BEVA 371 solution and BEVA 371 film in the conservation of skin and leather. I appreciate very much the huge amount of work the authors put into this very important and useful report, and I congratulate them on a job well done.

However, as inadvertently happens when dealing with a large, complicated subject, there are several details that require corrections:

• On page 343,2.1: Ketone N is a condensation product of cyclohexanone (not cyclohexane).
• 2.1: The exact formula for BEVA 371 was first handed out to all those present at the 13th AIC Annual Meeting in Winterthur, Delaware, on June 1972. It was presented at the IIC Lisbon Congress, published in its Preprints (1972), and later reprinted in Conservation and Restoration of Pictorial Arts (Berger 1976, 179, Butter-worths, London). The amount of toluene in the original formula was 1,000 g to make 1 gal. of BEVA 371 with no xylene. In the 1975 article quoted by the authors, I prepared a different mixture where I used 625 g of toluene and 375 g of xylene to make 0.5 gal. of adhesive for the project at hand. It turned out to be more difficult to use than the original formula, so I gave up. Unfortunately, I failed to mention this experiment, and I regret having caused this misunderstanding. Xylene was sometimes used as a retarder when the BEVA solution dried too fast.To achieve the desired ratio of 40% solids to 60% solvents, we later reduced the amount of toluene to 850 g and added 15 g naphtha, thus making it a total of 1,110 g of solids to 1,665 g of solvents per 1 American gal. of adhesive.
• 2.1: Laropal K80 is a homopolymer of cyclohexanone.
• Page 344: Hawker reports correctly that the Adam BEVA film and BEVA solution were “later found to have a modified formula, and were no longer authorized to be produced.” However, it was not that simple. I took him to court and, in order to prevent him and others who followed from using the name “BEVA” for their own mixtures, I got permission from the Kress Foundation to register the trademark BEVA in my name. Therefore, when using the name BEVA for the first time in a report, one should include the registration symbol to denote that it is a registered trademark. A footnote should indicate that it is registered in the name of Gustav A. Berger. Later usage of BEVA 371 does not need to repeat the trademark symbol.
• Page 353, 4.1: “… BEVA 371 heat-set continued to predominate over all choices.” BEVA 371 is a heat-seal adhesive, i.e., it is reversible, as opposed to a heat-set adhesive, such as epoxy, which is irreversible. Throughout the article, the term “heat-setting” of BEVA is used instead of “heat-sealing” (pp. 349–50, 3.2.1, and elsewhere). I have seen the same misnomer used by other authors as well. I therefore refer the readers of JAIC to another letter to the editor titled “On Hot-Melt, Heat-Seal, and Hot-Set Adhesives,” which I wrote 25 years ago (JAIC 18[1]:44–45).
• Suppliers: The address for Conservator's Products Co. has changed. The current address is P.O. Box 601, Flanders, N.J. 07836; tel/fax (973) 927-4855.

We would like to acknowledge and thank Mr. Berger for his letter about our article “BEVA 371 and Its Use as an Adhesive for Skin and Leather Repair: Background and a Review of Treatments” (JAIC 42[2]:341–62). His comments are very interesting, and we are glad that he wrote to clarify certain points. In fact, we would like to take this opportunity to thank Mr. Berger for his extensive contributions to the field of conservation, as his work has had a great and long-lasting impact on its advancement.

We were particularly interested in his comments about the use of terms “heat-seal” and “heat-set,” and they forced us to search out glossaries in encyclopedias and handbooks for definitions of these terms. For the reader's clarification, we submit the following definitions from seven different adhesive/plastic sourcebooks:

Hot-Setting Adhesive:

An adhesive that requires a temperature at or above 100�C to set it (ASTM 2003; Encyclopedia of Polymer Science and Technology, Plastics, Resins, Rubbers, Fibers 1964; Landrock 1985).

Heat-Seal:

To bond or weld a material to itself or to another material by the use of heat. This may be done with or without the use of adhesive, depending on the nature of the materials (Encyclopedia of Polymer Science and Technology, Plastics, Resins, Rubbers, Fibers 1964).

The use of heat reactivation to prepare a joint with a thermoplastic material present, as a thin layer, on the adherends; bringing adherend surfaces to their melting point and bonding under pressure (Landrock 1985; Shields 1976).

Heat-Sealing:

Method of joining plastic films by simultaneous application of heat and pressure to areas in contact. Heat may be supplied conductively or dielectrically (Harper 1992).

The process of joining two or more thermoplastic films or sheets by heating areas in contact with each other to the temperature at which fusion occurs, usually aided by pressure (Carley 1993).

Heat-Sealing Adhesive:

A thermoplastic film adhesive that is melted between the adherend surfaces by heat application to one or both of the adjacent adherend surfaces (Landrock 1985).

Hot-Melt Adhesive:

An adhesive that is rendered fluid by heat and forms a bond upon cooling. A hot-melt adhesive may be applied in any of the following states—molten, powder, or dry film (ASTM 2003).

Thermoplastic adhesive compound, usually solid at room temperature, that is heated to a fluid state for application (Harper 1992).

An adhesive that is applied in a molten state and forms a bond on cooling to a solid state. A bonding agent that achieves a solid state and resultant strength by cooling, as contrasted with other adhesives that achieve the solid state through evaporation of solvents or chemical cure. A thermoplastic resin that functions as an adhesive when melted between substrate and cooled (Landrock 1985).

Heat-Activated Adhesive:

A dry adhesive film that is rendered tacky or fluid by application of heat or heat and pressure to the assembly (ASTM 2003; Harper 1992; Landrock 1985).

Thermoplastic:

A material that will repeatedly soften when heated and harden when cooled (ASTM 2003).

Susceptible to repeated softening by heating and hardening by cooling (Shields 1976).

Thermoset:

A material that does not soften on heating, as a result of being formed from an irreversible chemical reaction initiated by catalysts, heat, light, radiation, etc. (Shields 1976).

A cross-linked polymeric material (ASTM 2003).

Thermosetting:

Having the property of undergoing a chemical reaction by the action of heat, catalysts, ultraviolet light, etc., leading to a relatively infusible state (ASTM 2003).

Setting:

The solidification of the adhesive by physical or chemical processes (Gerhartz 1985).

In light of the definitions, the following can be said:

The definitions do not distinguish clearly between a “heat-sealing adhesive” and a “hot-melt adhesive.” Both mention “thermoplastic,” “film” or “adhesive,” “melted,” “molten,” or “fluid” state, and “heat.”

“Heat-seal” or “heat-sealing” appear to be the same process that bonds thermoplastic materials to themselves or to another material by heat. Most of the definitions say with pressure. Melting or fusion are also mentioned in the definitions.

In no definition of “heat-seal,”“heat sealing,”“heat-sealing adhesive,” or “hot-melt adhesive” is “reversibility” or “cross-linking” mentioned, and, in our opinion, it should not be implied.

In the sources cited, “heat-set” is never given as a synonym for “thermoset,” the correct term for cross-linking adhesives such as epoxy resin adhesives. Neither does it appear as a synonym for “heat-seal.” In our paper, rightly or wrongly, we used “heat-set” as a synonym for “heat-seal,” given the common usage in the conservation field. The term “hot-setting adhesive” is not appropriate, as it requires a temperature ≥100�C to set.

The terms “heat-seal,” “heat-sealing,” “heat-activated adhesive,” “heat-sealing adhesive,” and “hot-melt adhesive” are processes and adhesives relating to the typical melt-freeze curing systems as opposed to evaporation of solvents or chemical cure systems.

Judging from the above definitions, perhaps a better term to use would be “heat-activated adhesive.”

We hope this will clear up any ambiguity, and once again we thank Mr. Berger for drawing attention to this matter.

REFERENCES

ASTM. 2003. Standard terminology of adhesives, D907–03. Philadelphia: American Society for Testing and Materials.

Carley, J. F.1993. Whittington's dictionary of plastics, 3d ed.Lancaster, Pa.: Technomic. 233–35.

Gerhartz, W.1985. Ullmann's encyclopedia of industrial chemistry, 5th ed.Deerfield Beach, FL: VCH Publishers.A1:226.

Harper, C. A.1992. Handbook of plastics, elastomers, and composites, 2d ed. New York: McGraw-Hill. Appendix A.

Landrock, A. H.1985. Adhesives technology handbook. Park Ridge, N. J.: Noyes. 12–21.

Shields, J.1976. Adhesives handbook. Toronto: Butterworth & Co. 334–44.

Encyclopedia of polymer science and technology, plastics, resins, rubbers, fibers. 1964. New York: John Wiley & Sons.1:445–47.