April 10, 2017
Samples were provided by Benchmark Catalog. No assumptions for their reactivity or corrosiveness were made prior to testing. The following material testing procedures were followed:
1) Samples were prepared while wearing nitrile gloves to prevent any cross contamination or imparting of any materials that may affect testing. Small swatches of each of the materials to be tested were cut roughly 2” in length from the original samples provided by Benchmark Catalog. These samples were then placed in glass laboratory jars with screw-on lids. These jars were then labeled with the appropriate sample name and number. Labels were applied to the exterior of the glass jars and dated. (See attached photos for each type of sample.)
2) Tweezers were used to place one of each of the polished, degreased metal coupons of lead, silver, and copper in each jar. The coupons were never touched with bare hands. The metal coupon bags were kept sealed. Lead corrosion appears when the presence of organic acids within the atmosphere forms. These corrosion by-products are represented as a powdery white to a reddish brown material on the surface of the lead coupon. The sterling silver coupon is sensitive and reacts to sulphur within the atmosphere. This turns the coupon black and, in extreme instances, causes pitting and
etching of the silver coupon surface. The copper coupon reacts to chlorides, oxides and sulfur compounds within the test environment, forming a variety of corrosion compounds ranging from dark brown to powdery green or whitish precipitate on the coupon.
3) After the jars received metal coupons and a testing sample, a sterile cotton ball was placed within the same glass testing jar. This cotton ball received three drops of de-ionized water by pipette to create the elevated humidity for testing. It should be noted that the metal coupons, as well as the cotton ball, were situated within the jar so as to not come in direct contact with the test material itself.
4) Each jar received a sheet of aluminum foil over the opening of the jar to create the appropriate seal to the container. Over this aluminum foil, the metal cap was screwed down tightly, and in this way the jars were prepped for the testing process.
5) The twenty-two samples within their testing jars were transferred to a QL Model 10 lab oven. The jars were placed on wire metal racks within the oven. The oven was then maintained at 60 degrees Celsius for 28 days, as per the Andrew Oddy protocol.
6) At the same time as prepping the individual samples for the oven, a control jar for each sample was created. Tweezers were used to place one A-D (acid detection) strip into each control jar containing a sample of each of the materials without metal coupons. These jars were sealed and labeled in the same manner as the oven sample jars. The strips were never touched with bare hands. The A-D bags were kept sealed and out of the light. These jars were maintained in ambient room conditions, 68 to 70 degrees Fahrenheit for the duration of the test to determine if outgassing of contaminants would occur at room temperature. Strips react to acid vapors turning from dark blue to green to yellow. Test results often occur within 24 to 48 hours after testing begins.
7) An additional control jar was maintained with no sample or metal coupons. This control jar received one A-D strip and was sealed in the same fashion as the control jar and the high humidity, high temperature test. This single jar was used to provide air sampling that could be correlated to the other jars, as they were prepped at the same time, taking into consideration temperature and humidity relative to the conservation facility. The jar without a sample was labeled “control/air quality.”
8) Samples were removed from the oven. Samples were then evaluated by the use of a microscope. Samples were placed under a Bausch and Lomb Stereo Zoom Microscope, equipped with microscope mounted full spectrum light source.
9) All three coupons per sample were analyzed as follows: Coupons were removed from their discrete jars. Lead, silver and copper coupons were then analyzed to determine reactivity and corrosion products. The criterion for pass or fail is a visual evaluation. In order to pass the test, a material should cause no more corrosion on any of the metal coupons than caused by the reference blind (“control”) test. Corrosion of the different metals gives a clue by the way they respond to which gasses the materials emit. Silver is corroded by reduced sulfur-compounds and carbonyl sulfides, and lead is corroded by organic acids and aldehyde and acidic gases. Copper is corroded by chloride, oxide and sulfur compounds. A-D strips alter color when exposed to an acidic environment and, therefore, pH is established. Other gases will also cause various types of corrosion. These other corrosion gases were not directly identified within this testing protocol. A-D strips were analyzed against control jar and A-D color chart to determine exposure to acids and aldehydes.
Findings and Results
After 28 days, sample jars were removed from the oven and visually compared against the standard that was also held for 28 days as a control. Additionally, one jar with A-D strip was maintained as a blind control to evaluate air quality while running the test. This jar, as well as the control samples, were maintained at ambient room temperature and did not receive accelerated temperatures or elevated humidity.
As part of the visual analysis, test materials were photographed under raking light. The first image is the digital photograph of the tested material, after removal from the test jar. The second photo is of the test material with color card. This color card is to indicate if there have been any subtle visual changes to the material as originally provided by Benchmark. The subsequent three metal coupon photos are micrographs taken through a Bausch & Lomb stereo-zoom microscope with digital photo capture. Finally, the last photograph is an image of the A-D strip measuring organic acids. All micrographs were taken at a 10X magnification. LED raking light source was used during the microscopy portion of the evaluation.