Food irradiators as a method for sterilization for severe mold infestation on archaeological artifacts

Jim Roberts

Abstract

The challenge is to find a safe treatment which would not introduce moisture, yet effectively eradicate the mold, as well as its spores, not only on the surface but also behind historic linen tape mends, inside the cordage holes, and between the yucca fiber cordage for extremely desiccated and fragile willow mat fragments from the Chaco Anasazi culture.

Research into food irradiators indicates that sterilization with cobalt 60 would kill both the mold and its spores without harm to the organic structure of the mats. No residual radiation remains after the process.

Samples of mold from the mats were isolated on cotton swabs in sterile glass vials. These swabs were sent to Radiation Sterilizers Inc. where the mold was grown in petri dishes and subjected to radiation in order to determine the correct dosage.

A prototype of the storage/travel container was built. Together with a fragment of CHCU 2688, thoroughly documented photographically, the Ethafoam prototype was sent through the irradiation chamber. This second test controlled damage or change to the willow shoots, yucca cordage, or Ethafoam storage/travel containers. RSI tested the fragment for mold. After testing, the fragment in the container was returned to WACC for a thorough examination.

A uniform storage/travel container was designed with a beveled cut out, the inside of which could be “individualized” for each mat. The design parameters included the use of “on-hand” materials, uniformity of size, stability, built-in humidity controls, the ability to stand the container on end for irradiation treatment, and ease of access to the artifact.

The mats were cleaned mechanically, treated with 0.05% solution of orthophenyl phenol in ethanol, stored in the travel containers, irradiated in the containers, and shipped to the storage facility.