In this talk, Marianne Webb presented some findings from her ongoing research into the degradation of Asian lacquers.
She produced 11 different samples of lacquer formulated with Urushiol-based lacquer (sourced from Japan, China, and Korea), Laccol-based lacquers (from Vietnam or Taiwan), oil, and pigment. The sample boards were all prepared in the same manner, coated on both sides with raw lacquer, a layer with inert clay filler applied to both sides, and then ground smooth after drying in a wet box. The different lacquer formulations were then applied. The samples were artificially aged in a weather-ometer, exposing a new section of the sample each week for four weeks.
The degradation was evaluated using five factors: color, gloss, surface pH, autofluorescence, and microcracking.
Color – Fading was not a reliable assessment of degradation of black lacquer, but worked well for red lacquers. Microfadometer tests have placed red lacquers between Blue Wool 2 & 3, indicating that lacquer has similar light sensitivity to paper or textiles.
Gloss – Each sample had a different original gloss, with laccol on its own having less gloss than urushi, but becoming very glossy with the addition of oil. Transparent urushi retained its gloss well, but formulations with added oil lost a significant amount of gloss after aging.
Autofluorescence – chemical changes in lacquer seemed immediate once exposed to light (after 12 hours, the differences were obvious) but there is a maximum point at 1 week, then the autofluorescence decreases.
Surface pH – The pH of lacquer doesn’t necessarily drop as it ages. Transparent lacquer seems to have the lowest pH after aging because the light can penetrate it and therefore it gets more light damage. There was not direct correlation between the amount of oil and pH after aging, but they generally had higher pH. After approximately 1 week the pH reaches a plateau and then after 3-4 weeks it goes back up. Clearly, lacquer’s pH does not have a linear relationship to aging. Disclaimer: All pH tests damage the surface of lacquer since they require water to solubilize degradation products, leaving a void.
Microcracking – All of the samples showed changes after exposure to light. The patterns were distinct and all different.
The level of detail in the investigations and results of the study was incredibly impressive. The study emphasized the number of factors that one should consider when approaching each individual piece of lacquer. The author also indicated a desire to investigate formulations with Thitsi lacquer (from Burma and Thailand) and the sudden fogging phenomenon sometimes observed when lacquer is exposed to heat and moisture in the future.
Author: Raina Chao
44th Annual Meeting – Research and Technical Studies Session, May 16, 2016, “Combining RTI with Image Analysis for Quantitative Tarnish and Corrosion Studies” by Chandra Reedy
This talk focused on the combination of two technologies, Reflectance Transformation Imaging (RTI) and Image analysis. Much of the talk dealt with the application of these two technologies to evaluate accelerated aging or Oddy Test coupons in a quantitative manner. As the evaluation of Oddy tests has traditionally been subjective, making reproducibility problematic, I was particularly interested in the potential for quantitative analysis.
Reflectance Transformation Imaging (RTI) is a relatively inexpensive and simple tool that creates a mathematically synthesized image of an object’s surface from a series of image (typically ~36) lit from different angles and directions. The image produced by the RTI software can reveal visual information that is difficult to discern under normal conditions.
Image analysis software utilizes algorithms that enhance the visual separation of features and marks them for analysis, a process known as segmentation, thereby enabling those features to be quantified. The software used by the authors of this presentation was Image Pro Premier by Media Cybernetics, which has previously been used for thin section analysis of ceramics.
The authors used RTI and Image analysis in combination to evaluate Oddy test coupons. The process aided in visual assessment, improved the documentation of the results, and provided quantitative results. Adding RTI and Image analysis to the Oddy test protocol was not a cumbersome addition, requiring only ~ 20 minutes. It was noted that the type of coupon used made a big difference for this technique, as foil and bent coupons were not ideal since the added texture complicated interpretation of the results.
After exposure, the coupons were photographed and processed in batches by metal: silver, copper, and lead. A single image of the coupons was chosen from the RTI viewer and used for image analysis. A different protocol was used for each metal. The image of the lead coupons was converted to grayscale and the colors inverted, background, control, and corrosion areas were defined, and the “Smart Segmentation” tool used to separate and quantify them. The image of the copper coupons was not converted to grayscale and the variety of corrosion types were all treated the same by the segmentation process. The image of the silver coupons was converted to grayscale or pseudo-color to enhance differences before segmentation. The software allows for individual segmentation protocols to be saved and reused. The percentage of tarnished to untarnished surface could be calculated for each metal. Comparison with visual evaluation of test coupons yielded the following results:
Control or clear pass: 1-4% tarnish
Clear Fail: 45-100% tarnish
Pass for temporary use: 7 – 17% tarnish
The “temporary” category is particularly hard to judge when evaluating Oddy tests in the traditional manner, so this method seems to be especially useful in this case.
In addition to Oddy test results, RTI and image analysis were used by the authors to evaluate rapid corrosion tests and coating tests. In each case, like with the Oddy tests, the process provided good documentation as well as the possibility for quantitative results. The combination of these techniques seems to have great potential for a number of applications and their relative simplicity and inexpensiveness make them a great tool for institutions with limited analytical capabilities.