Volume 18, Number 2 .... May 1996

TECHNICAL EXCHANGE

Aquazol: One Conservator's Empirical Evaluations

At last year's AIC meeting in St. Paul, Mark Lewis and Richard Wolbers presented a paper on the Evaluation of the Suitability of Poly (2-ethyl-2-oxazoline) as a Potential Retouching Medium for Easel Paintings. After the presentation, Mark mentioned that Richard had also experimented with this versatile polymer as a consolidant for hinterglasmalerei. In an earlier study Poly (2-ethyl-2-oxazoline), otherwise known as Aquazol, was determined to have the same index of refraction as glass (1.520) and found to be exceptionally stable after accelerated aging tests. As I seem to attract this particular art form with depressing regularity, I began my own experiments.

The product is manufactured by Polymer Chemistry Innovations and is currently available in three molecular weight grades: 50 (MW50,000), 200 (MW200,000) and 500 (MW500,000). All three grades are highly soluble in many polar, organic solvents, such as: acetone, ethanol, and water. I found the lowest grade to be soluble in isopropanol or ethanol with the addition of some water. As an adhesive, the Aquazol 500 is more useful, although I have not found it to be strong enough to consolidate heavily deformed paint.

My experiments on glass have found that the Aquazol 50 and Aquazol 500 form excellent films, and dry water white. However, while the Aquazol adhered very well to the glass, it did not uniformly adhere the paint to the glass. I would welcome comments from colleagues on this procedure, as my own results are not conclusive.

Another application that I have been experimenting with is the admixture of Aquazol 500 (10-20% solution in water, w/v) to watercolors for inpainting. Simply mixing a small amount of Aquazol medium provides enough gloss to facilitate more direct color matching. This technique is especially useful for inpainting abraded areas, rather than over fills where the mixture tends to become very glossy and pasty when too heavily built up; in which case, the Aquazol 50 can be used. So far I have not noticed any incompatibility between the Aquazol and the gum Arabic or any problems with surface tension when varnishing over this medium. Major advantages are that no pigment grinding is necessary and no toxic solvents are used. Obviously, this technique is entirely empirical and should be properly tested.

I have also used Aquazol 500 as a binder for calcium carbonate to make an easily carved filling compound. It also works well in a dilute form when texture needs to be "painted" on.

Aquazol Physical Data:
Glass Temp.: 69�C-71�C (amorphous)
Refractive Index: 1.52
Appearance: Light Yellow Solid
Specific Gravity: 1.14
Melting Point (Amorphous): 110�C-120�C
pH in Aqueous Solution: Neutral
Solubility in Water: Freely Soluble
(The three grades of Aquazol mentioned above can now be obtained from Conservation Materials, Ltd.)

An Electric Power Engraver for Removal of Old Fills

Recently I was faced with the removal of a great deal of overfill (approx. 20% of a 130 cm x 100 cm picture's painted surface) from a 17th c. Dutch painting on canvas. The overfill may have been applied to cover shrinkage damage possibly caused by an early glue lining. This is evidenced by the tight raised edges of the previously cupped paint. Though six different filling materials from separate interventions could be identified, the mass of the overfill was of one type, a pigmented oil/chalk compound, insoluble, hard and brittle. Mechanical removal was the only option.

However, even when working under high magnification, either a scalpel or an abrasive glass engraver's tool would nick or scratch the underlying paint. Alternatively, the fill would pop off safely under the pressure of a round knife, though small bits would remain. These were more difficult to remove and considering the size of the picture, manual removal brought with it the fear of carpal-tunnel syndrome developing long before the cleaning was completed.

A solution was found using an Electric Power Engraver with an extra fine solid carbide point. The engraver used was the professional model (Record Power Ltd., Sheffield, England) which is rated for continuous use, an important factor as other models work 15 minutes on/30 minutes off. In contrast to Dremmel-like tools which spin, the engraver oscillates. The amplitude is adjustable and the stroke rate is 100 times per second. At the amplitude necessary for the fill removal the movement was barely felt when touched to a finger.

The brittleness of the fill material in relation to the softness of the paint made it possible to fracture the fill material by just touching the tip of the engraver to it. Damage to the original paint could only occur by applying great pressure or by scratching with sideways movement.

A great time saver and safe for the original paint, the fine tip also made it possible to remove tiny bits from the smallest interstices of the paint. Not all the different fill materials flew off as easily but the tougher ones could still be carved away easier using the engraver than with a manual tool. Additionally, a variety of tips are offered with power engravers--points, abrasives, chisels, gouges and ball points--any of which may be helpful in a variety of tasks.

Web Site of Interest to Conservators

My all-time-favorite web site is that of the TV program "This Old House", located by going to the PBS home page. It contains a great deal of useful information on tools and new products, how to buy them and how to use them. For instance: I found a description of a "plastic twine" dispenser, which spools out a three inch wide strip of Saran-like material, perfect for strapping or clamping odd-shaped objects. It also features a free bulletin board for queries and problems, and contains many links to other preservation organizations, primarily related to architecture.