Problem Solving in Paper Conservation

When I talk to new acquaintances about conservation, I receive an alarming number of immediate comparisons with the National Treasure films, capers that blend American history, conspiracy theories, and Hollywood glitter.  I assure these acquaintances and all current readers that these movies have very little in common with the field of conservation.  But in the spirit of adventure films, I’ll begin today’s post with a quote from the fictional, swashbuckling archaeologist Indiana Jones:

“Snakes.  I hate snakes.”

Why start here?  Because Jones’ longstanding antipathy toward his slithering nemeses parallels my professional feelings about an increasingly common foe: the white glue commercially known as Elmer’s.

For repair purposes, archives typically use water-soluble, reversible adhesives like wheat starch paste.  These adhesives are ideal because they allow previous repairs to be undone when needed, such as removing a silk lining from a paper document.  Reversibility is a central concept in modern conservation, but this wasn’t always the case.  Items that were repaired many years ago, or were repaired by dealers or collectors, were often subjected to whatever materials were on hand.

Lately, I’ve encountered a number of documents lined with silk and a combination of paste and white glue.  At first glance, these documents give no cause for alarm.  But once placed in a bath, the linings remain stubbornly adhered in tiny spots all over the document.  Closer examination then reveals small, milky-white spots of glue, swelled by the water, but not fully reversed.

What’s a conservator to do?  Simply put, get creative and use chemistry.  We know that Elmer’s glue, and white glue in general, is much like the common bookbinding adhesive PVA.  And we know that a Teas chart is a tool that maps various solvents according to their solubility parameters.  Let’s find a Teas chart for PVA, and then, through careful testing, let’s see if any of the solvents effective on PVA will work on our white glue.  Bingo: ethyl acetate.

Ethyl acetate seems to work best when the white glue has already been swelled with water.  It evaporates quickly, so it requires quick, localized work.  But I’ve found it to be quite helpful in removing linings and reducing residual adhesive afterwards.  Treated items receive a final water bath to flush any remaining solvent.  I’d be very curious to hear from other paper conservators any experiences, thoughts, or concerns about using ethyl acetate in this way.

One last personal observation on white glue: it only seems to appear on high-profile treatments involving especially famous or valuable items.  And it appears on these items more regularly than even Murphy’s Law would dictate.  My theory is that these highly valued items have been highly valued for many years, and as a result, their past treatments were probably designed to be extra strong.  If someone incorrectly thought that a water-soluble adhesive might be a weak adhesive, then perhaps that person might have added some white glue to their paste for good measure.

Or perhaps I just have bad luck. I’ll watch out for snakes.