Co-authored by Elizabeth DeBold (Curatorial Assistant), Renate Mesmer (Head of Conservation), Austin Plann Curley (Book Conservator), and Adrienne Bell (Book Conservator). With special thanks to Kevin Cilurzo (Conservation Intern).
As some of our respondents observed in their comments on this month’s Crocodile Post, there is a strange-looking deposit on the leather of this book.
The book is, as others correctly identified, one of the volumes from the Folger’s multi-volume set of Famiglie celebri Italiane…, an eighteenth-century work published in Torino, which focuses on Italian heraldry. Recently, one of our curators noticed that several volumes in our vault had developed a strange, white deposit, and reasonably assumed it was mold. Following our protocol for finding potential mold, we prepared to seal the affected volumes in plastic, and contacted our conservators. All while trying not to panic. “Mold” is one of those words that strikes fear into the hearts of every librarian.
Fortunately, based on their experience, our conservators were able to allay our fungal fears, and told us that what we thought was mold was likely something entirely different. They still wanted to test their theory, which (as you will see in the video below), turned out to be correct. The white deposit is something called “spew” (or spue), also known as “leather bloom” or “fatty bloom.” Although this condition sounds serious (and disgusting), it’s actually a non-damaging reaction that occurs in some leathers which have been treated (or “dressed”) with different fatty or waxy compounds. When the leather is exposed to a change in climate, these unbound compounds migrate towards the surface and solidify, where they form a crystalline residue. This residue is the “spew.”
To test whether the deposit was spew as suspected, our conservators applied heat to a sample taken from the binding to see if it would melt (spew typically changes from a solid to a liquid under low heat). If it was not spew, there would likely be no change, and they would know the residue was something else. The residue did melt away, though, confirming their diagnosis. In the video below, sample of the spew collected on the tip of a fine needle melts under low heat on a hot plate (it starts very slowly but picks up speed as the video goes on):
Only a handful of volumes in our collection are currently showing evidence of spew, possibly because we recently lowered our vault temperature by 10 degrees as part of a grant-funded preservation project. Low temperatures extend the life of different materials significantly, including paper, wood, and leather.
We’re not sure why these few books are showing spew while the rest of the collection is not. Not all of the volumes in Famiglie celebri Italiane are showing the residue, while other volumes stored in different places in the vault and unrelated to Famiglie celebri Italiane are. Here are two other examples that we found:
The volumes of Famiglie celebri Italiane are bound in similar leathers, but the skins might not all be produced identically. Another reason for this phenomenon could be due to dressing the leather, which was a common practice into the late 20th century, including at the Folger. We don’t have any treatment records for the volumes affected with spew, don’t know if they were ever treated here, and if they were, whether that treatment included dressing the leather.
Of course, our library staff knows (and you should as well) to never assume—if you see something strange and are unsure of what it might be, always take steps to confirm its identity so that you know how to proceed with proper treatment, if necessary. In the case of the spew here at Folger, our conservators will carefully wipe it off with a soft cloth to avoid removing any leather.
To learn more about spew check out these resources:
The Alaska State Museum. “Leather and Skin.” What’s that White Stuff? Caring for Alaskan artifacts (blog).
McLean, William. “Leather ‘Bloom’ – Causes and Remedies.” Skin Deep: the biannual Newsletter from J. Hewit & Sons Ltd, no. 2 (1996): 19-20.
North Carolina Department of Cultural Resources. “Less is Usually More.” North Carolina Connecting to Collections (blog).