John Delaney discussed the \u201cyellow filter\u201d model for virtual cleaning and compared it to experimental results from measurements of cleaned paintings before and after treatment.\u00a0 To estimate the result of removing a discolored varnish, conservators sometimes correct the color using imaging software, \u201csubtracting\u201d out the varnish as if it were a yellow filter.\u00a0 The experimental values were collected using FORS (fiber optic reflectance spectrometry) of specific points and hyperspectral imaging of the entire surface of the paintings.\u00a0 The specific values for the\u00a0 “yellow filter”\u00a0 for a given painting is taken from the absorbance spectrum of the removed varnish and then applied to the rest of the painting. \u00a0After examining the spectra before cleaning, after cleaning, and the estimated virtual cleaning, it was clear that the yellow filter model for virtual cleaning was not enough to explain the spectral changes seen after cleaning.\u00a0 After varnishing the cleaned area, there was no change in color, only an increased brightness indicated by a rise in the near-infrared signal, so that alone did not explain the additional component missing from the yellow filter model.<\/p>\n
I was thinking that even if it wasn\u2019t spectrally perfect, could the yellow filter model at least be a good tool for an estimation of results?\u00a0 The example of the 15th<\/sup> century Tuscan panel convinced me otherwise\u2014while the yellow filter worked well for the blue areas, the model was a poor estimate for the red and brown areas.\u00a0 One component that is not taken into account with the yellow filter model is the effect of scattering by the varnish.\u00a0 Aged varnishes don\u2019t just yellow, they also increase the scattering of light.\u00a0 Even with a scattering model included, the yellow filter model still did not accurately reflect the results of removing a yellowed varnish.<\/p>\n While virtual cleaning with simple \u201cyellow filter\u201d color correction in image processing software such as Photoshop is cheap and can be somewhat informative, it certainly is not a perfect model for varnish removal, even when the yellow filter\u2019s spectrum is taken from the actual discolored varnish.\u00a0 The study has not considered selective cleaning, grime removal, or other nuances of cleaning paintings, which would only further complicate the spectral correction.<\/p>\n","protected":false},"excerpt":{"rendered":" John Delaney discussed the \u201cyellow filter\u201d model for virtual cleaning and compared it to experimental results from measurements of cleaned paintings before and after treatment.\u00a0 To estimate the result of removing a discolored varnish, conservators sometimes correct the color using imaging software, \u201csubtracting\u201d out the varnish as if it were a yellow filter.\u00a0 The experimental … Continue reading “39th Annual Meeting – Paintings Morning Session, Friday June 3 – “An Experimental Study on the Merits of \u2018Virtual Cleaning\u2019 of Paintings” by John Delaney”<\/span><\/a><\/p>\n","protected":false},"author":68,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_exactmetrics_skip_tracking":false,"footnotes":""},"categories":[2,34,16],"tags":[70],"class_list":["post-656","post","type-post","status-publish","format-standard","hentry","category-annual-meeting","category-paintings","category-specialty-sessions","tag-aics-39th-annual-meeting"],"_links":{"self":[{"href":"https:\/\/resources.culturalheritage.org\/conservators-converse\/wp-json\/wp\/v2\/posts\/656","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/resources.culturalheritage.org\/conservators-converse\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/resources.culturalheritage.org\/conservators-converse\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/resources.culturalheritage.org\/conservators-converse\/wp-json\/wp\/v2\/users\/68"}],"replies":[{"embeddable":true,"href":"https:\/\/resources.culturalheritage.org\/conservators-converse\/wp-json\/wp\/v2\/comments?post=656"}],"version-history":[{"count":0,"href":"https:\/\/resources.culturalheritage.org\/conservators-converse\/wp-json\/wp\/v2\/posts\/656\/revisions"}],"wp:attachment":[{"href":"https:\/\/resources.culturalheritage.org\/conservators-converse\/wp-json\/wp\/v2\/media?parent=656"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/resources.culturalheritage.org\/conservators-converse\/wp-json\/wp\/v2\/categories?post=656"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/resources.culturalheritage.org\/conservators-converse\/wp-json\/wp\/v2\/tags?post=656"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}