Hi,
I am interested in experimenting with straight Canada balsam as a varnish. The Getty Art & Architecture Thesaurus (link below) says that historically it “was found to bloom in moist conditions and darken with age.”
My questions are: 1) Does the color darken to gray/black or to red? 2) What humidity level triggers blooming? 3)What would the treatment for bloom be?
Thanks!
Thank you. And then how would one go about removing a natural resin varnish that covers a work done in tempera/distemper?
Canada balsam is a poor resin for use as a varnish today as we have a group of very reliable synthetic resins that remain stable and colorless over time. It is certainly clear to begin with and has little color. However, I have paint outs of a large number of resins and the Canada Balsam has yellowed over time. Its primary use was not as a coating but as an adhesive to hold cover slips on microscope slides. It worked well for this before modern synthetic, and superior resins were developed. If you obtain old slides you can see that it has yellowed to some degree on these as well.
As to bloom, I am not sure of any study that has shown at what RH the Canada balsam blooms. It was never a common resin for varnishing and, therefore, there was no impetus to do the study. Mastic resin certainly had the reputation of blooming in humid conditions. BTW, I do not recommend using any natural resin varnishes. They just cause too many problems for future conservation.
As to the treatment of bloom, the varnish needs to be removed. Other past treatments such as reforming, etc, cause far more issues than they solve.
Just leave it alone. A conservator in 30 years can deal with it. Just please record your painting system and the Canada Balsam coating somewhere on the painting to aid thier efforts.
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