Thanks to Doug Nishimura, Senior Research Scientist at the Image Permanence Institute, for his contributions to this post.
Ethafoam is closed-cell foam made from polyethylene and often recommended as a preservation-appropriate material for making object mounts. C2C has recommended this product, visited an NC factory supplier as part of a mount-making workshop, and used it for hands-on storage-mount-making practice in volunteer training. Conservation testing and materials research in the last decade, however, suggest caution when it comes to ethafoam’s use with metals.
R. Scott Williams, Senior Conservation Scientist at the Canadian Conservation Institute has warned that direct, long-term contact between polyolefin and polyethylene foams and metals can lead to corrosion. (Read his report here by scrolling down to pages 26-29 & 31-33.) Williams notes that the variety of foam manufacturers leads to an uncertainty about the chemicals involved in its processing. Often retailers substitute the product of one foam supplier for another, assuming that products with the same texture and appearance are the same. More and more, Chinese factories are the producers of polyolefin and polyethylene foams, and different manufacturers use various additives. Additionally, blowing processes can be either physical or chemical and result in a similar appearance. These apparently minor differences, however, can yield varying long-term preservation results.
During our workshops, we often hear questions about the long-term stability of colored foams, such as pool noodles. Williams’ research indicated that pigments do not pose a danger to the long-term stability of the foam. Pool noodles are a reasonably safe product for storage-mount-making. The one exception to the safety of colored foams is the light pink foam, indicating anti-static properties. The anti-static agents migrate to the foam’s surface and are made from fatty compounds that can trap moisture and speed metal corrosion in cases of long-term contact.
Recent oddy testing of ethafoam with metal coupons has reiterated concern. Tests resulted in a striated pattern of corrosion on metal coupons when in direct contact. There was no noticeable deterioration from foam vapors (i.e. nearby, but no direct contact). Conservators, therefore, recommend a barrier layer between the foam and any metal object. In C2C hands-on exercises we have used tyvek (pictured above), white cotton jersey, and colored poly fleece. All three materials are soft and stretchy enough to smooth the surface of cut foam (which can be very abrasive) and tuck into slits cut in the foam. Because tyvek (also made of polyethylene) is not a blown product, it does not pose a metal corrosion danger in contact. Conservators’ research and cautions about contact between ethafoam and metals mean that these barrier layers are an important preservation measure, helping to prevent both abrasion and metal corrosion.
Posted on August 20, 2013, in collections care, Connecting to Collections, storage, workshops and tagged Hibco Plastics, oddy test, polyethylene, polyolefin, pool noodles, Scott Williams, tyvek. Bookmark the permalink. 3 Comments.