The Bullerswood is the grandest of all the hand-knotted carpets made by Morris & Co. It dates to 1889 and is based on ancient Persian and Turkish carpet samples collected by Morris. It has woolen pile on a cotton warp, is colored with vegetable dyes, and is HUGE, approximately 4 meters by 7.5 meters (13 feet by 25 feet). It is currently on view in the British Galleries at the Victoria & Albert Museum.
The carpet is rarely displayed and its colors are still vibrant. While researching the carpet I found a fascinating article about how scientists have determined the ideal display and lighting conditions for this masterpiece.
The vegetable dyes used in the carpet "range from reasonably light-fast to very fugitive." (What a great use of the word fugitive!) The curators must consider that the "brighter the illumination, the easier the object will be to see but the greater the rate of light-induced deterioration." What to do? The approach was to carry out a series of experiments on the back of the carpet. Sections of different colors were brightly illuminated over time intervals long enough to detect fading by measuring spectra of reflected light with a spectrophotometer. Unexpectedly, they discovered that the blue areas on the carpet faded the most with the least fading occurring for burgundy, opposite of what is typically the case for objects colored with vegetable dyes.
The V&A has developed a lighting policy which establishes acceptable fading rates for artifacts, namely that changes be limited to one 'just noticeable fade' (JNF) in 50 years. After a very technical discussion of how one measures a JNF (a new unit for this scientist) the article concludes that exposure for the carpet would need to 19 years of display at 50 lux to conform to the policy. As the light level in the gallery is 100 lux, it was decided that the carpet would be on display for only 5 years, a length of time which allows for errors in the above calculations as well as preserving the possibility of a further five years display over the next half century. Pretty interesting! I now realize how lucky I was to even get a glimpse of this beauty.
Morris notebook sketch of design for Bullerswood Carpet