A translation of the index card reads "'This photograph on cotton is light and wash proof.' 'This photograph is unique because only two copy's of this procedure [technique] exist. The other one is still owned by the photographer. This photograph is light and wash proof. Made in 1923.'
I'm indebted to Marieke de Natris (Documentalist Portrait Photography 1840-1920, RKD, 18 Jan 2016) for bringing this to my attention.