CONSERVATION OF WATERLOGGED IVORY

From the Santa Margarita

By

MAURO T. ALVAREZ

Field Archaeologist/Conservator

The Ivory objects excavated at the Santa Margarita Wreck site are mostly carved religious Images; a few are for utilitarian, functional or decorative purposes.

Condition of the Objects

After four hundred years under-water, they are waterlogged. Some were found to be well protected by sand; others are covered with concretions, many have metal and organic stains or are physically damaged by violent storms on the reef.

Conservation

First Aid Conservation

From the site these objects were initially immersed in tap water/ sea mixture for a period of two weeks. This was then followed by soaking in tap water.

Laboratory Conservation

Cleaning. Prior to the desalination process, the objects were immersed in a solution of 3 % Acetic Acid in water for one day to remove the concretions on the object. In some cases a soft artist brush was used to remove the concretions, followed by immersion in tap water to remove the acid from the object. Water was changed every day. Every time the water was changed, an acid test was done using pH paper. Once the paper yielded non acidic water, removal of acid from the objects was completed. To remove stains, 3% Ammonium Hydroxide was used for copper stains, for iron stains 3% Oxalic acid and 3% Hydrogen Peroxide, all of them mixed with water. After all of this was performed, depending on the problems mentioned, the objects were immersed in tap water for one day.

Desalination. Soaking in tap water was the initial step in the desalination process. Every two weeks the tap water was replenished, each time prior to the changing of tap water a salt test was performed using silver nitrate solution. A comparative test was also performed on the source of the tap water to determine the amount of salt extracted from the artifacts. When the results became even or the color of the source and the soaking   solution became the same, desalination of the ivories using tap water wasl then elevated to salt free mineral water. The same process was done until the salt test yielded  negative results.

Dewatering process. When the desalination was completed the artifacts were immersed in a series of water/methanol mixture to displace the water with alcohol to be used for the consolidation. The alcohol was used as a solvent during the consolidation process. This process was done in two weeks starting from a mild concentration of methanol, increasing it to 100% methanol thus displacing the water entirely. The objects remained in the alcohol one week to be sure the alcohol fully displaced the water.

Consolidation. Prior to the consolidation process, initial weight of the objects was recorded. From the alcohol the ivory objects were immersed in a solution of 5% PVA Resin in Methanol. The time table for the consolidation of the objects varied depending upon the rate of absorption: a shorter time for very porous material, and longer for hard and compact material.  Every month the weight of the objects was noted until such time that the weight of the consolidated objects became constant. The object were then dried.

Controlled Drying. The objects were dried in a controlled environment to slow the drying of the alcohol and resin.

Application of Protective Coating. The objects were then coated with 8 % PVA Resin in Methanol.

Restoration. Broken pieces were joined together with a gel of cyanoacrylate based adhesive.  Remaining small gaps were filled with Plaster of Paris (high grade) mixed with PVA Emulsion.

Scraping Excess Filler. Excess filler was removed by scalpel blade and a mild sanding.

Retouching of Color. Filled up parts were retouched using oil color mixed with xylene.

Application of Second Coating. To come up with a uniform texture the restored objects were coated with 5% PVA Resin in Methanol solution.

Salt Test. This test was performed by pouring 25 ml soaking water, 3-5 drops of 3% Nitric was added, followed by 1-3 drops of 1% Silver Nitrate solution. The intensity of the effervescence determined the amount of salt extracted.

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