Volume 16, Number 2, May 1994, pp.19-20

Technical Exchange

Construction Materials

wood

High Density Overlay (HDO) is recommended by Jean Tetreault and Scott Williams of the Canadian Conservation Institute as preferable to MedEx or Medite II, because the impregnated Kraft paper covering appears to form a reasonable barrier against acid migration, based on chemical prediction, though not on testing. (Medite II is advertised as formaldehyde-free, but is still western softwood, and will still outgas.) Another advantage to HDO is that because it is based on Douglas Fir rather than particle board, it is structurally stronger; this allows a thinner piece to be used, which off-sets the higher cost of HDO. HDO is sold as Ainsworth HDO, Duraply HDO, or Permaply HDO; it is intended for use as reusable concrete-pouring forms.

sealants

film: MarvelSeal 360 (nylon-aluminum-polyethylene laminate) is being carried by University Products; MarvelSeal 470 (polypropylene-aluminum-polyethylene laminate), as recommended by Dennis Piechota, may have longer-term stability. MarvelSeal 1311, also recommended by Dennis, has a brown paper backing which is convenient for adhering with wallpaper paste.

Deborah Bede of the Boston MFA reports on an adhesive coated polyester sheet for sealing materials like Gatorboard and Masonite, The Research Lab tested its effectiveness as a sealant, and found it to be excellent. Long-term aging properties are not known, but acrylic adhesive and polyester sheet bode well. The material is Flexmark PM 150C, a paper-backed glossy film which is transparent and easy to peel and apply (from Flexcon Company, Wall Street, Spencer, MA 01562; (617) 885-3973.

Pam Hatchfield, also of the active MFA, describes the use of Camger clear finish 1-146-40 waterborne polyurethane glaze. It can be sprayed on, but requires 2-3 coats. Short-term effectiveness appears good; again, realtime aging takes realtime... Available from Chemical Systems Inc., 364 Main St., Norfolk MA 02056; (508) 528-5787.

J-Lar tape (by 3M) is used by many exhibit designers for case sealing; Martin Burke of the NPS suggests that it may be safe as a temporary seal. Reports on extraterrestrial use are not yet in.

Tom Brown Inc Construction Adhesives in Castle Shannon PA (412) 884-2121 provides custom-cut strip adhesives useful for case gaskets. Call and ask for Sales to discuss your need.

Silicone vs. Rubber Gaskets

How to tell if a gasket is made from silicone rubber or organic rubber: Color is no longer a deciding factor: black is usually associated with organic rubbers, and clear with silicone rubbers, however, many silicone gaskets are deliberately colored black. The best "quick and dirty" method for differentiating rubbers is the burn test: take a small piece of the material and burn it in an open flame. The silicone rubber will usually only burn when in the flame and will powder white or gray on the surface. The smoke from the burning silicone is usually white. The organic rubber will burn more rapidly and continue to burn when removed from the flame. It leaves a dark powder on the surface and emits blackish smoke. (Note: observe safety precautions below) There is usually more ash produced when burning silicone rubber than organic rubber. The silicone rubber burns white because silicon dioxide is forming from the burning of the long silicon oxide chains. The organic rubber ash is often black because of the presence of carbon in the rubber. There is little if any carbon in silicone rubber. When conducting any burn test normal lab precautions should be followed. Do the test in a fume hood or equivalent well ventilated space, and make sure there are no flammable materials nearby. The burned sample should be extinguished in a dish of water so it will not cause a hazard when disposed.

Silicone rubber gaskets are available from: Delta Design, PO Box 1733, Topeka, Kansas 66601, (913) 234-2244

APS Inc, 5235 Snapfinger Woods Dr., Decatur, GA 30035, (404) 808- 4111

Netherlands Rubber, 2931 Exon Ave, Cincinnati OH 45241, (513) 733-0883

Threads for Textile Conservation

Lacis, an East Bay textile shop (materials, antique textiles) supplies some very unusual threads which textile conservators would be pleased to obtain. They do mail order and will answer specific questions re thread weight, ply and color by telephone [ed. query: can they color match by phone too?] Not all the threads are always in stock. Threads come in a variety of natural, ecru and whites, sometimes black. Cotton: 80/2 up to 170/2; linen: 30/2 to 140/2; silk 30/3-200/2 and 800 filament silk. Lacis 2928 Adeline St., Berkeley CA 94703 (510) 843-7178

New Restoration Colors Available

Golden Artist Colors has released a line of Mineral Spirit Acrylic (MSA) restoration colors. The paints will fill the place on your palette and in your heart where Bocour Magna colors resided. But this is an unfair comparison, Golden's MSA colors are much, much better tempered (pardon the pun).

The paints are more finely dispersed than were Magna colors. Some colors are smooth and creamy out of the jar although others are a bit stringy. However, when diluted with the proper solvent, all handle nicely. When thinned down with solvent, they flow off the brush like fine watercolors. We have had a few weeks to evaluate the colors for conservation work. When used from a dried palette with the paints reactivated with solvent, the paint has none of the stringiness and stickiness characteristic of Magna colors. The fine grind of the pigment gives an immanently workable paint.

For conservation uses, the paint regenerated from a dried palette is well balanced to fat in consistency. For an even glossier paint additional medium can be added. While not endorsed by Golden, Arkon P-90 in Stoddard solvent worked very well as an added medium.

The paint medium is n-butyl methacrylate in a mixture of Stoddard solvent and aromatic 150, an aromatic hydrocarbon mixture. 58 colors are available, all are of either excellent or very good lightfastness for normal interior exposure. Alizarin crimson is not available having been substituted with quinacridone crimson. An interesting color is the quinacridone gold, a very transparent yellow-brown which should do very well for matching discolored varnish. The fresh paints are compatible with (and technically reversible in) very low polarity solvents. To be used from a dried palette, however, Stoddard solvent and VM&P naphtha are not sufficiently polar to regenerate a workable paint. More polar solvents like Shell Sol TS-28 (75% aromatics) or, even better, xylene are required to recover a paint that flows cleanly off the brush. It should be possible to find a mixture of solvents which will have the desired polarity with a lower aromatic content.

The colors are sold for professional use only and are not intended for use by children or household use. While the paints do not bear ASTM D-4236 labeling, each jar is labeled "WARNING: COMBUSTIBLE. INHALATION MAY BE HARMFUL. CONTAINS: PETROLEUM DISTILLATES. See MSDS prior to use." The fresh paint has a moderately strong mineral spirit odor and you might want to dry your palette in a fume hood or outside.

The paints are distributed in glass screw cap vials in 1, 4 and 16 ounce sizes. Because conservators use such small quantities of paint, we have some concern that the paints might dry out over prolonged storage. Golden is testing the efficiency of the coated cardboard lined metal lids. Even if the colors were to dry out, they can be reactivated by addition of solvent.

Conservation Support Systems is the exclusive distributor of the MSA line to the conservation market. Prices for the MSA line range from $5.70 to $10.10 for the 1 oz. jar, depending on the pigment. Orders of 10-19 jars receive a 10% discount and over 20, 15%. The complete set of colors (1 oz.) are available for $327.15 ($349.45 with a wooden storage box) which represents a 25% discount on the individual jar price. A hand painted color chart is available for $1.00.

Also of interest, Golden Artist Colors is developing a line of solvent based PVA colors. For more information on either product, contact Scott Blair at:

Conservation Support Systems
P.O. Box 91746
Santa Barbara, CA 93190
(805) 682-9843.

[ed note: it may be helpful to check the long-term redissolubility of n-butyl methacrylate against your intended use.]

Containers

Sippin' Saver Beverageware by Rubbermaid is a spill-proof square polyethylene bottle with comfortable hand grip, with a flip-up pouring tube in the cap which locks securely in the closed position. (An additional internal straw is used for drinking.) Available in 8 oz, 16 oz, and 32 oz sizes. All sizes were on sale recently at Ben Franklin dime stores for $1.00 each. For safety's sake you should probably decide whether you will use these for sipping or slopping, and not have both available in the lab.

Support Gloves

Handeze Energizing and Therapeutic Support Gloves are claimed to alleviate hand and wrist pain. call 1-800-432-4352 for your nearest Dome dealer. (They also make home and office record books such as bookkeeping and auto mileage logs, and accounting software for DOS computers.)

Russian Sturgeon Glue

The use of sturgeon glue for the treatment of paintings used to be a matter of myth and dreams for conservators in the United States. Thanks to recent political changes, this caviar of adhesives is now available from a number of sources, including Andrew Andreev in Moscow.

The adhesive is extracted from the dried inner membrane of the air bladder of the sturgeon. It is traditional to prepare the glue directly from the dried air bladder. Full instructions for the preparation and use of the glue can be found in the article by Tatyana Petukhova and Stephen D. Bonadies, "Sturgeon Glue for Painting Consolidation in Russia" in the Spring 1993 issue of the Journal of the AIC (Vol. 32, no. 1, pp. 23-31).

Quantities as small as 100 grams may be purchased. The approximate price is from $100-500 per kilogram, depending on the amount purchased and the quality of the adhesive. Write or fax for a price quote on the amount of adhesive desired.

Andrew Andreev Ak.
Artsimovich St.,
16/378 Moscow, Russia
tel./fax: (007) (095) 3366296
or
c/o (818) 787-0419