7 IMMERSION

IN IMMERSION TREATMENT the entire object is submerged in a bath of solvent, which acts upon the tape to remove the carrier if it has not been previously removed, the surface adhesive, and any resins that have migrated into the paper. The proper choice of solvent allows the conservator to selectively remove the undesirable tape and adhesive without altering other parts of the object.

Immersion offers several advantages. It is usually quicker and more efficient than other methods. In fact, speed and timing are very important to its success. It is often gentler than other methods, since the object is subjected to less manipulation, and nothing is added other than volatile solvents. The danger of surface scrubbing is largely avoided. Because of the large amount of solvent used, tide marks are much less of a problem, and stubborn adhesive residues may often be more effectively removed than with other techniques. Finally, apprehension about the long-term aging of a sheet treated locally and thus, perhaps, locally modified in its aging characteristics, is not a factor.

Immersion is ideal for single leaves of small to moderate size that have no solvent-soluble components in either the pigments, inks, pencil, ownership stamps, or paper, including dyes, sizes and fillers. When large quantities of tape are involved, immersion is certainly the treatment of choice wherever possible. Immersion is in appropriate for bound volumes and for items with solvent-soluble components and should not be used where a fume hood is unavailable.

7.1 Equipment

The technique of immersion follows a series of simple steps. First, solubilities are determined by using the local procedures already described, and the best-suited solvent is identified. Next, the equipment and supplies needed for treatment are assembled at the fume hood. An effective, disposable tray may be made from a sheet of polyester film (such as Mylar or Melinex) with the edges folded up and fastened at the four corners with staples. When long soaking time is anticipated, a stainless steel or enamel tray is preferable. The tray should be sufficiently larger than the item to facilitate handling, but small enough to minimize solvent use. Polyester support sheets (either non-woven fiber such as Hollytex or Pellon, or film) should be cut slightly larger than the item, and a polyester film sheet cut to cover the bath if the solvent is a fast evaporator. In addition to small lifting and scraping tools, the conservator will need cotton swabs, a brush, blotters slightly larger than the item, and a stack of 3″ � 5″ blotters. The solvent chosen for treatment should be available in sufficient quantities for several baths, held in a container that can be lifted comfortably. Last but not least, appropriate safety equipment should be used, including goggles, gloves not affected by the solvent, and a standby respirator in case it is necessary to work with one's head in the hood. With all the necessary equipment assembled one is ready to begin. If possible, the tape carrier has already been removed by using the procedures described earlier.

7.2 Procedure

Pour solvent into the tray approximately �″ deep. Quickly slide the object into the bath. Hesitation can result in tide marks. Watch the item and manipulate the tray by rocking gently.

After a few seconds, if the carrier has not been previously removed, try a corner with a tool. If it moves easily, lift it away. If not, wait a few seconds and try again. Remove the carrier as soon as possible. With luck, any remaining residue will be swollen and soft. If there is suspicion of residue, tip the tray to expose the adhesive mass and search for it in raking light. If there is residue, scrape it gently or roll with a swab. This should be done as soon as possible. Sometimes, especially with precrosslinked acrylic tape, the longer the residue swells and softens, the greater the chance that soft polymer will be trapped in the paper structure and subsequently be more difficult to remove. Acrylic adhesive scraped from the object must be transferred to waste blotter so that it cannot redeposit elsewhere on the object being treated.

When the residue appears to be gone, quickly lift the object on its support from the tray to a waiting blotter. Blot quickly. Be wary of the tape area. Most of the adhesive should have been removed, but it may be sticky still. Lift off the top blotter and look for any differential evaporation or sheen revealing remaining residue. If residue is still present, repeat baths as needed.

Rubber-based adhesive may need longer soaking times and may require several changes of bath. Sometimes a subsequent bath in a different solvent will diminish a stubborn stain. For example, if the carrier and surface adhesive come off in toluene, the crosslinked resins deep in the paper may respond to acetone.

7.3 Risks

Immersion treatment is not without risk, and one should be aware of what can go wrong.

Inks that were stable during testing may start to move in the course of treatment. Correction in this case requires judgment. Sometimes it is safest to pull the item from the bath immediately. Other times it is best to wait until the movement has gone to completion and to keep the tray rocking gently. When the color stops moving, then pull the item. The latter approach is appropriate when the bleeding dye is a minor component whose loss does not significantly change the body tone or intensity of the ink.

Introduction and removal of the item from the solvent must be quick, even, and complete or tide marks may form which won't move later.

Too strong a draft may take the item up the hood as it dries. Watch closely, or anchor a piece of polyester web over the surface during drying.

One final warning: Before starting an immersion treatment go over the steps carefully and gather equipment for any possible occurrence. Once the treatment is underway, the conservator cannot safely turn away or leave until the treatment is finished.