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Conservation treatment - Case Study - Conserving the Skull of Diplodocous

Posted on Tuesday, March 17, 2009 in Uncategorized

by FeiWen Tsai
Department of Paleobiology
National Museum of Natural History
Smithsonian Institution

The following is a brief description of the stabilization of one of the exhibited ink wash drawings,”Skull of Diplodocus, lateral view”, which needed conservation treatment in preparation for exhibition in the Dinofest 1998 art show, Drawn from the Earth. The illustration was moved to SCMRE for stabilization prior to exhibition. In addition to being unstable, it was dirty and discolored to a yellowish brown color, probably from long exposure to excessive light and humidity. The illustration was examined by a conservator, who recorded the drawing’s description, condition and treatment needs on a treatment proposal form, as indicated below.

This photo shows the illustration of the skull of Diplodocus before treatment.

This photo shows the illustration of the skull of Diplodocus before treatment.

The illustration was composed of the black ink wash drawing and several notations in other media. These included the field accession number 1631and catalog number 1921 written in graphite pencil on the upper right corner. Stamps reading “From US National Museum Washington USA” in blue ink were impressed on the recto upper left corner perpendicular to the image and on the verso, diagonally near the center, of the illustration. The substrate of the illustration was characteristic of a mixed-pulped paper and had several features that appeared to be part of the original construction of the drawing. Pinholes located at the corners might indicate that the illustration had been attached to the table during tracing or on the wall for display. [Note: Ridgway, 1938, recommends that the drawing paper be "laid down with thumbtacks or dampened and pasted along the edges"]. Scratch lines around and in the “eye hole” areas of the image might have been made by the artist.

In addition to the general yellowing of the substrate, there was an adhesive stain with a piece of tracing paper sticking to it on upper left side of the illustration. Knife cut marks, apparent outside of the image area, might have occurred when a researcher, tracing the illustration, scored tracing paper while it was directly on the top of the illustration, with the knife occasionally slipping through. In fact, a drawing on tracing paper that matched the outline of the knife cuts was later found in the folder. Some short, arc-shaped creases (handling dents), resulting from improper handling, were present throughout the illustration. Other creases, as well as tears and losses, were found on non-image areas.

Treatment Recommendations
Because many losses and tears occurred along the edges of the illustration, mending and filling were necessary to stabilize the illustration’s condition. This allowed the drawing to be handled and framed safely without putting more stress on damaged areas. The following was proposed to stabilize the drawing:

Surface cleaning - This is the first necessary step before other treatments. It minimizes abrasion from accretions and prevents dirt from being imbedded into paper fibers during subsequent wet treatment, such as washing or mending.

Mending - This closes tears and reinforces physical weakness caused by tears.

Filling - This inserts similar materials into losses to fill and strengthen the substrate.

Matting and Framing - This protects drawings from direct handling and harsh environments.

Initial Procedures Before Stabilization

Photodocumentation and Solubility Tests - Before starting stabilization, the condition of the illustration was documented using both color slides and black/white film (Fig. 13). [Note: This process was repeated again after the illustration was stabilized, so that there would be a permanent record of the drawing before and after stabilization.] The paper and ink were tested to record their properties and reactivity in response to various solvents. This initial process helped determine treatment methods. As a result of the testing, it was found that the blue ink used to stamp the drawing was extremely soluble in water.

Selection of an appropriate surface cleaning methods - Various cleaning methods were tested, such as using a soft hair brush, grated vinyl erasers, and a vinyl eraser block, on small areas of the verso. These procedures were carried out under a stereo microscope. The paper’s surface was not extremely porous, so the grated vinyl eraser method was chosen because of its gentle, less abrasive cleaning properties.

Preparation for Filling - Three different types of Japanese tissue with similar textures to the drawing were selected for possible insert materials. Toning was necessary to match the color of the illustration. This process is primarily cosmetic; it allows the object to be viewed without visual disturbance.

The method of toning was as follows: acrylic pigments were mixed to a desired color and then diluted with water to form a solution in a tray. The selected Japanese tissues were floated on the colored acrylic solution in the tray for few seconds, followed by air-drying. The tissues were then rinsed using deionized water to remove loose pigment particles, then dried again under blotters and weight.

Because the insert tissue is much thinner than the illustration’s paper substrate, several pieces of tissues were laminated (adhered together) to the same thickness as the illustration in order to be more compatible with the drawing. Adhesion was done using dilute wheat starch paste.

Stabilization Procedures

Surface Cleaning - The illustration was surface cleaned using grated vinyl erasers and a soft hair brush on non-image areas. Eraser crumbs were brushed off to prevent abrasive and discoloring residues being left on the illustration. Cleaning was carried out cautiously around areas of image, pencil marks, and tears to avoid removing any original markings or further damaging tear areas.

Mending - Mending and filling were carried out on a light table. During mending, the illustration was placed on the top of the light table to align tears and close gaps using wheat starch paste applied by tipping in spots of paste with a fine-pointed brush. After the tears were aligned, a mending strip of feathered, pasted Japanese tissue was placed on the verso to reinforce each tear.

Filling - Selected laminated tissue was laid on the top of the polyester film, which was placed between the illustration and the repaired tissues. The outlines of losses were traced using a dull needle on a light table. After tracing, the excess part of the laminated tissue was torn away and the shaped fill was then aligned and inserted into the loss area using wheat starch paste. Because the repaired areas looked very clean and new, “cosmetic surgery” to tone down the edge of repair was conducted using pastels and a paper stump.

The photo on the left shows the illustration of the skull of Diplodocus after conservation treatment was complete.

The photo on the left shows the illustration of the skull of Diplodocus after conservation treatment was complete.

Matting and Framing - The illustration was attached to a backboard of acid-free archival quality matboard using Japanese tissue and wheat starch paste. The attachment method, called a T-hinge, consisted of two strips of tissue representing the stem and cross-bar of a “T”. Two small vertical rectangles of Japanese tissue were adhered with dilute wheat starch paste along the top edge of the verso of the illustration to form the stems of the T-hinges. The drawing and hinges were then aligned on the backboard. Each hinge stem was secured to the backboard by overlaying it with a pasted and larger horizontal cross-bar of Japanese tissue. This allows the drawing to be removed from its backboard at some future date by cutting around the stem of its hinge. The illustrations were sent back to the Paleobiology department for framing using UV filtering plexiglas and an aluminum frame.

After it was matted and framed, the drawing of “Skull of Diplodocus, lateral view” as well as the drawing of “skull of Diplodocus, posterior view”, and the drawing of “skull of Diplodocus anterior view” were shipped by a fine arts moving van for exhibition in the Dinofest art exhibit.

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