“What colour is this thread?”
That was the question that I posed to Danny, a visitor who came to the Dalton and Colour Vision event held during Manchester Science Festival in October.
“Brown”, he said.
I found this incredibly interesting, because I saw the thread as green.
Danny was one of several visitors that day that had red-green colour blindness, the most common form of the condition. It was first described by famous Manchester scientist John Dalton in a 1798 account entitled ‘Extraordinary facts relating to the vision of colours’. In this account, Dalton said of his own colour blindness:
“That part of the image which others call red appears to me little more than a shade or defect of light. After that the orange, yellow and green seem one colour which descends pretty uniformly from an intense to a rare yellow, making what I should call different shades of yellow”.
Chris, one of my fellow volunteers on the day, was showing a piece of red sealing wax, thought to belong to Dalton himself, and a picture of a green laurel leaf to another family. “Dalton would have seen this wax as the same colour as this leaf”, he told them.
“Does that mean he would have seen green as red as well?” the father asked inquisitively.
This was a common question asked by visitors, but the answer is very complex and depends on the severity of the colour blindness. As volunteers, we didn’t really have the expertise to tackle such a big question, but it was great to see visitors’ curiosity piqued by these special objects.
Testing for colour blindness
Dalton wasn’t the only researcher in colour vision. Some 73 years after Dalton’s death, in 1917, Professor Shinobu Ishihara from the Imperial University of Tokyo published a set of 38 colour plates as part of the Ishihara colour test (as part of the event, we showcased a later set, published in 1948, and many of the adults who visited us said they remembered the plates from their school days).
Meanwhile, in Victorian England, a doctor named Frederick Edridge-Green developed the Edridge-Green colour bead test, which was later adopted by the Royal Navy in 1912. However, this came several years after another colour vision test, called the Holmgren wool test, had already been developed, specifically for train drivers.
“It was devised by a Swedish scientist, following a railway accident that they believed was caused by the driver’s colour blindness”, Lyn, another volunteer, told a group of children with their accompanying parents. She was showing them how to make a weighted sample of coloured wool thread, which would then be used as part of a giant version of the Holmgren wool test. “The test would have been like this”, she said, gesturing to the railings from which hung several dozen coloured wool strands, “with different coloured samples of wool laid out, and the person being tested would be given a sample of pale green wool, which they would then have to match to the nearest colour”.
All in all, we had an impressive total of 258 strands hung up on the railings, with which visitors could test themselves.
John Dalton conducted a colour test of his own that involved describing the colours of five silk threads in his notebook. We invited our visitors to write down what colours they thought these five threads were. The most common answers were green, red/pink/orange, brown/red, blue and purple.
We also had two gentlemen with colour blindness take part in the study. Their observations were as follows: brown/brown; red/orange; dark red/red; blue/dark blue; and light blue/mid blue.
It was very interesting to compare the results, particularly between those with normal colour vision and the ones with colour blindness. We had a lot of variation in descriptions too; for example, dark olive green, russet red, chestnut brown and cobalt blue.
The colour thread study proved extremely popular, while the event overall allowed us to marvel at just how differently we all see from one another. To quote Lyn, “The topic of colour blindness is fantastic, as everyone had heard of it and/or knew someone who had it, making it very relevant; the public felt connected and appeared interested.” Through the work of Manchester’s own John Dalton and other researchers in the field, we hope we have inspired our visitors to consider different perspectives from their own, as well as having encouraged more communication with and observations of the world around us.
Image credits: Olivia Hemingway