hide glue

“Tortoiseshell and Imitation Tortoiseshell” Monograph — New To The Archive

Recently while working to impose order to the library of the Barn I came across a pile of articles needing scanning and formatting for posting to the web.  “Tortoiseshell and Imitation Tortoiseshell” was my contribution to a 2002 conference that required travel to Amsterdam for the presentation itself, in complete disregard to one of my personal mottoes, “If I ain’t at home, I’m in the wrong place.”

The scanned article is now in the “Conservation” section of the Writings section of the web site.  There are two versions, one about 4.5 megs and another about 1.5 megs.  I’m still working through the idiosyncrasies of my scanner and compewder, figuring out what settings work best.  If I can get this better I will upload that version later.

Gelatin Molds For Plaster Casts II – Ye Olde (and new) Apothacary-ness

Developing, or more precisely re-developing, technology that was once common practice requires lots of mental noodling sprouting from the question, “Really, how did they do that?”  In the end it all comes down the the world we artisans inhabit, the world of Applied Materials Science.  Fortunately for me the base material, hide glue, was plentiful in the shop so I had plenty of raw material to work with.  In the pursuit of gelatin molds for cast ornamental plaster my proof-of-concept work revolved around the observations of how molten hot hide glue (the “gelatin”) actually cures into a rigid adhesive layer and the changes in physical properties while en route.

As cooked glue goes from hot liquid to hardened mass the first step is the one of greatest importance for this undertaking.  At a particular point in the process — exactly where and when depends on a number of factors including the concentration of glue solids dissolved in the water, the grade of glue, the ambient temperature, relative humidity, barometric pressure, and probably phase of the moon — the molten glue mass forms a semi-solid gelatin, which is the stage I am interested in both exploiting and maintaining in stasis.  As long as the mass stays flexible it can be used and re-used as a molding material.

A  major concern for this practice is that the gelled/flexible mass be water resistant.  Though that seems, and is, obvious the accomplishment of that feature requires a bit of forethought.  If casting plaster is the end goal, and for me and the ancients it was, the mold for holding the plaster as it was poured and cured had better be able to withstand the incursion of the copious quantities of water involved.

A second consideration is that the gelled mass, once transformed from an amorphous blob into a detailed mold, be tough enough to impart said details and allow for the set plaster casting to be de-molded without destroying the mold itself.

And finally, in order to be used repeatedly the gelatin mold must be preserved over some indefinite period of time.

Reflecting back on protein chemistry and historical craft/art practice I conclude that the ancients accomplished all three of the previous items more-or-less in one step: they added the most potent protein crosslinker/preservative they could find, formaldehyde.  It has long been understood that exposing or incorporating formaldehyde into collagen matrices renders them water-resistant, or “hardened.”  Think embalming.  Think taxidermy.  Think of the ancient practice of exposing bowstrings and wrapping to the smoke of a wood fire, from which formaldehyde is a by-product.

Since formaldehyde is so noxious I do not have it in my chemical inventory and instead relied on another chemical from the world of film-based photography that performs an analogous function of crosslinking or “hardening” gelatin films.  In practice I found this to be an admirable option for a couple reasons, and not so good in another,  Not problematic per se, but requiring another consideration.

To be sure the photographic gelatin hardener performs admirably in imparting water-resistance and integral toughness to a gelled mass.  I observed it also extends the timeline for the gelled state considerably, apparently retarding the water egress that turns gelled collagen into a hard, glass-like film.   This was perhaps my (and their) first ace in the hole.  A second observation beneficial to the process was that the plaster itself, being integrated into and reacted by water, served to moisten and thus keep the mold flexible   Every time plaster was cast into the mold, it re-plasticized the mold mass.

However, the current safer chemistry of the gelatin hardener does not impart the same biocide/preservative effect that was accomplished previously by formaldehyde.  Thus my initial mold attempt turned into a rotting mass of oozing slime in a few days.  Not an un-solvable problem, but a stinky, sticky mess.

Back to the drawing board.  Sorta.

Next time – Ye Whole Sheebang.  This time with lots of pctures.

Gelatin Molds For Plaster Casts

A couple months ago I was sent a question about using gelatin molds for casting architectural plaster.  I had seen references to the technology in several of my old books but did not possess any that provided a decent description of the material or the process, so I noodled it a bit.  I’m not an architectural historian per se, so there might be plenty of old books with the exact information.

For the past almost forty years I have relied on silicone RTV molding rubber and never saw the need to broaden that horizon, but this question prompted me to undertake some exploring.  I am awfully glad I did as I now have another potent arrow in the quiver.

Of course at issue were several considerations.

  1.  The gelatin (hide glue) would need to be used in the semi-cured state, in other words after it had gelled and had not yet lost enough water to enter the more solid phase of a dried, cured mass.
  2. The gelatin mold had to be firm/flexible enough to actually cast plaster into it, then have the casting de-molded ex poste.
  3. The mold needed to be robust enough for repeated using.  The literature references using the molds dozens or even hundreds of times.
  4. Finally, the mold needed to remain viable while not becoming a giant fur-ball of mold.

Thanks to a timely failure of a tordonshell batch I gleaned the path to success, when combining that experience with some noumena from my wanderings into materials science.  The ultimate result was a high performance molding material that was also cheap.

The trek included a number of face palm moments in discovering new ways of working.

Stay tuned.

Talkin’ Hide Glue Magic

Recently I spoke to both the Washington Woodworker’s Guild and the Professional Refinisher’s Group, a/k/a “Groop,” on the topic “Decoding Hide Glue.”  This marked 33 years since my first talk to WWG, and I have spoken many times at previous Groop gatherings over the past two decades.  (Anyone even marginally interested in the art, technology, and craft of wood finishing should belong the the Groop forum where finishing problems and techniques are the coin of the realm.)

This presentation was — for me — a delightful romp through the materials science of protein polymers, including their description and derivation and the many routes of modifying them that can directly influence practices at the workbench.

The presentation began with a description of the term “gram weight strength” which in turn begins with the rendering of the animal parts, then walking through the use implications of the different grades.


I covered the basics of how glue works, and how the components of adhesion contribute to the success or failure of the system.

I discussed in some detail the modifiers used with glue, including plasticizers, gel suppressants, crosslinkers, and preservatives, wrapping up with moldmaking and casting.

Fortunately thanks to my friend JohnH the Groop presentation was recorded almost in its entirety (~99%) and I will work on getting it posted on line.  I did not get the camera settings perfect but the information is all there.

Stay tuned.

Flexible Gap Filling Adhesives (video)

Recently I was making a presentation to a group and afterwards one o the attendees approached me and told me that he enjoyed my youtube video,   As he described the video I was perplexed until I realized it was not my video, it was from The Getty Conservation Institute, a video of a presentation I made almost a decade ago.

I do not recall ever posting it here before, and if I did this already I apologize for the redundancy.  I hope you laugh in all the right places,

The Writing Desk Drawer, A Tale of Woe

During the time I was working on the fancy veneerwork for the legs, the drawer had been sitting minding its own business at the other end of the bench.  Unfortunately and unbeknownst to me in those intervening weeks the finished drawer, complete with matching veneer and bead edge, decided to act like an elected official and go crooked on me.  When I picked up the drawer to put it back into the writing box I saw that it had racked and twisted almost 1/2″ from corner to corner and would only go into the runners part way.  I could have dealt with 1/16″ with a little bit of shaving and a little bit of shimming.  But this require pretty drastic intervention.

The problem was both vexing and perplexing.  I had specifically selected a piece of very old tulip poplar for the structure of the drawer, yet here it was, gone all potato-chip-ie on me.  At the very least I would have to trim the dovetails and hope I could get it all back together, flat.  The edge beading that trimmed the edges of the drawer face was completely sacrificial and I knocked that off with a mallet and chisel in short order.  An hour in a water-filled trough released the rear dovetails and the back slat of the drawer, but the front was a trickier issue.

My first and foremost consideration was NOT damaging the veneer on the front of the drawer as that was carefully matched to the surround on the desk.  If I screwed that up I would have to saw a whole new piece of veneer from the prized figured plank, and I had zero interest in that.  Since the veneer had been applied to the curved front of the drawer with hot hide glue all it took was immersing it in hot water and letting the glue line relax to remove the veneer and get to work solving the problem.  No problem, right?  We’ve all heard this was the Achilles Heel of hide glue, that it was not robust and prone to failure in high-moisture environments.  I placed the drawer face down in a plant trough and poured in the hot water.  I checked back in a few minutes and nothing had happened.  Well, the finish had bloomed but that was irrelevant.  The veneer was holding firm.

I did it again.

No change.

And again.

No change.

I left it in the water trough overnight and checked it again in the morning.

Still firm.

In aggravation I dried off the drawer front and removed all the shellac finish.  Using my tacking iron and spatulas I rubbed the heated iron (over a wet rag) on the face of the veneer and gently worked the spatulas underneath the veneer to separate the glue line.  It worked, but took over an hour of nerve-wracking time.

I set the veneer aside, undamaged but a little warped as you might expect.  But certainly salvageable.  I put the drawer front back into the water trough overnight and was able to disassemble the dovetails to see where I could trim the joinery to get it to fit snug and flat.

But for whatever reason this piece of clear, vintage wood had twisted and there was nothing I could do to un-do that.  I won’t describe the whole process of trying to re-use and re-fit the original components — I think I have exasperation induced amnesia on this chapter of the tale of woe — but in the end decided to build a whole new drawer front.  The drawer sides and back were just fine, but that bowed drawer front was, as my beloved Mom might say, a stinker.  (My mother is among the most gentle, even tempered people I have ever met, and I never heard an uncouth word cross her lips.  She once, however,  described a troublesome co-worker as, “A real stinker,” and I knew he must be The Spawn of Satan.)

So I fabricated new new drawer front from a different piece of lumber, also vintage tulip poplar, cut new half-blind pins, and reassembled the whole.  New edge beading, relaid the veneer, and newly finished.

It was perfect, and held true until the desk was finished and delivered.  Whew.