The Wonders of Nature and Art

Well, it seems that the mysterious covering material used on a Fitzwilliam Museum Persian manuscript does indeed fit Thomas Smith's description from 1803:

Thomas Smith, ‘The wonders of nature and art: or, A concise account of whatever is most curious and remarkable in the world; whether relating to its animal, vegetable and mineral productions, or to the manufactures, buildings and inventions of its inhabitants, compiled from historical and geographical works of established celebrity, and illustrated with the discoveries of modern travellers, Volume 4, 1803

I've recently finished conserving MS 18-1948, a sixteenth century edition of Nizami's Haft Paykar, given to the Fitzwilliam Museum in the early 20th Century. It is covered with a very peculiar textured skin, dyed green on the surface with a copper-based colourant, with a white core visible in areas of damge. The manuscript came to attention for conservation due to the broken and failed historic leather reback which had left the beautiful illustrated manuscript unsupported, unsuitable for research or display, and vulnerable to damage.

The covering material (left) is now brittle and unforgiving. There were losses in association with the historic leather reback, and the corners had been repaired previously. Faced with this unusual binding, and in light of the fact that it would require rebacking once again as part of my treatment, I sought to identify it.
My colleague, Paola Ricciardi, was able to carry out non-invasive material testing as part of the MINIARE initiative here at the Museum. Unfortunately, technical examination with both FORS and XRF were inconclusive.  Paola could see strong signals for copper, and from the gold painted decoration, but the true nature of the substrate remained illusive.
As this textured material was not behaving like leather, I was reasonably confident that it was not anything which might be described as Morocco. The raw-hide characteristics and texture suggested it may be Shagreen- a material I believed to be shark or ray skin- but the ID challenge was further compounded by the fact that I couldn't see the back of the covering material where Margot Brunn at the Royal Alberta Museum, Canada (thanks DistList) said the characteristic fibrous structure of ray or shark skin would be visible. This leads me to another problem, the fact that when researching the identity of this material, I started to look for Shagreen.
As I mentioned above, I believed shagreen was a raw-hide prepared from shark or ray skin. However the descriptions in historic sources, including Thomas Smith's publication from 1803, described a textured material which was certainly not made from pelagic sea creatures. At first I took this to be a confusion or misunderstanding of true production methods of this unusual material, but when I looked up shagreen in the OED, I found that it was described as:

a) A species of untanned leather with a rough granular surface, prepared from the skin of the horse, ass, etc., or of the shark, seal, etc., and frequently dyed green. Also, an imitation of this. 

b) The skin of various sharks, rays, etc., which is covered with close-set calcified papillæ, forming a hard rough surface: used for polishing, etc.

...All of which is very helpful, I'm sure you'll agree(!). It seems that shagreen has been used as a general catch-all term for any knobbly or textured skin.

The final clue leading to the identification of the material covering the Fitz manuscript came from an unlikely source- an article shared by a friend from the BBC news site (apparently my friends think of me when they see news about shoes).
In the article published earlier this year, 'Why did men stop wearing high heels?', a pair of men's 17th Century Persian shoes are illustrated. Their green colour and knobbly texture looks very much like the binding of MS 18-1948 and the caption describes them as being 'covered in shagreen - horse-hide with pressed mustard seeds.' Having seen this I got in touch with Karen Vidler at Book Conservation Services. Could this possibly be true? Surely texturing skin with mustard seeds was a bit far fetched? Karen confirmed that it was probably a material know as Persian shagreen, described in John Waterer's, Leather In Life, Art and Industry, 1946. In Waterer's account, shagreen is not made from shark or ray skin, but is the name for a method of decorating parchment resulting in a characteristic pebbly pattern without a distinct grain. This could be tested with a Ferric spot test to check for the presence of plant phenol groups. Their absence confirmed that this material was not tanned. It seems that Smith's description of the production technique is feasible, he was only incorect when he states that 'the skin [is] then tanned.'

With the identity of this unusual covering material confirmed, I was able to complete my treatment of the manuscript. I chose to reback the repaired spine with a Japanese paper laminate to ensure the historic boards and Persian shagreen covering material were physically strengthened and supported, whilst also maintaining a clear differentiation between this historic covering material and my modern repair.
So, a parchment textured with mustard seeds. I would love to know if this material is still produced anywhere, or if there are further accounts of its production. I probably need a field trip...

MS 18-1948 after treatment.Open showing the first two illustrations (left) and closed showing the upper board and reback (right)