In his book, Bonom (Vincent Glowinsky) shares a little more details about the work. 'Tirage argentique sur papier baryté, 50,8 x 61 cm' is what it says beneath this piece. Translated to English, that description would be something like  'silver print on baryta layered paper'. 

If you are, just like me, not familiar with that term, I got you covered! This is what google told me: The paper he used is a high qualitity type of paper used for art/ photo purposes. This paper brightens the color of the print. It last incredibly long, from 60-300 years, I read. That might be why the artwork is in such a great condition today, 10(+) years later.