Protein Glues: What's The Difference?

Simple Chart: Temperature Vrs. Viscosity

I have spent my entire career as a woodworker using protein glues exclusively.  I have lectured and written lots of times trying to explain their advantages.  Features like reversibility, easy clean up, relatively low cost, quick or long open time as needed, bonding to itself, transparency to stains and finishes and, above all, no danger of working with toxic chemicals make it my first choice.  Protein glues are, by their very nature, organic.

Still, I get calls every day from woodworkers new to these adhesives asking simple questions.  Since the answers are generally the same I thought I would post a quick page for general information.

All protein glues have a common feature.  They react only to heat and moisture.  If you understand that concept then you can easily make them do what you want.  If you have a problem it is because you do not have both heat and moisture at the glue surface in the proper proportion.  If the viscosity is not right then check the heat and moisture ratio and adjust.  If the glue sets up too quickly or too slowly then consider the environment and make changes.

Consider that all antique furniture was made with protein glues, and craftsmen were often working in cold unheated workshops in winter.  So how did they manage to assemble furniture if the glue set up quickly.  Obviously, they were experienced and prepared for each operation by having all the clamps ready for the job.  Also, since the water component of the glue is the part which carries the heat, they realized that cold dry wood surfaces would quickly draw the water out of the glue and make it tack.  Therefore, they often used a hot wet rag to wipe the joint surface just prior to applying the glue.  The water molecules in the pores of the wood would prevent the glue from setting quickly, without actually diluting the glue strength.  I use this method for all large assembly projects where I need a longer open time.

Simply put: You add water to the glue and then heat it.  It sets by first cooling (which provides a tack) then by drying out (loosing moisture).  Protein glues are friendly molecules with lots of Hydrogen bonding sites so they easily hydrate and can be modified by a large number of other chemicals which can bond at these open Hydrogen sites.  Protein glues bond to protein glues, so an old joint with glue residue can be cleaned with a water wash and new glue will bond to the glue residue with both molecular and mechanical adhesion.  Synthetic glues do not do this.

Hide glue and Glue Pot

Hot Hide Glue (HHG)

There is one company left in America making hide glue: Milligan and Higgins.  Their website is www.Milligan1868.com.  You can find a lot of technical information there, and you can call them and speak with Jay Utzig, who is their chief chemist, with your questions.  He is always happy to talk about glue.  They sell wholesale only.

Hide glue is sold by "gram strength" which is determined at the factory by measuring the glue with a Bloom Gelometer.  Gram strength has nothing to do with the adhesive strength of the glue, so a higher or lower gram strength does not mean a stronger or weaker bond.  Gram strength is determined by how much force (in grams) it takes to depress a plunger a certain distance into the glue.  It ranges from a low of 50 grams to around 500.  Low gram strength glues take longer to set and are flexible and high gram glues set quickly and are brittle.

Woodworkers generally use gram strengths in three groups: 192, 222, and 251.  I have always used 192 and find it works well in general for all my uses.

Traditional Sheets of Protein Glue

It is available in sheets (traditional), pearl or granulated form.  I like the granulated as it has a larger surface area and is quicker to hydrate.  In a dry state, it has an unlimited shelf life.

HHG must be cooked and used hot.  You need a double boiler.  It doesn't matter if the double boiler is copper, stainless steel, porcelain or iron.  Just find one on Ebay and get to work.  Get a cheap hot plate, a common stainless steel meat thermometer and a glue brush.  Add cold water to the glue, wait about 15 minutes for it to gel and then heat it up to 140 degrees.  Do not heat above 160 degrees.  Keep a thin viscosity during use by adding water the same temperature as the glue.

I use HHG for all quick setting work, like rubbed joints, hammer veneering and assembling marquetry on an assembly board.  I used to use it on all furniture making and repair but now I use Liquid Hide glue for that work.

Liquid Hide Glue

Liquid Hide Glue (OBG)

When I was involved with an international marquetry conservation group in Paris in the mid 1990's I participated in research which modified HHG using Thiourea to extend the open time.  Since Thiourea is a carcinogen I did not want to work with it.  However, Urea is not toxic and the only difference between the two is a single Sulphur molecule.  I began to experiment with Urea to modify the glue and eventually was able to formulate a liquid protein glue which I named Old Brown Glue.

Franklin Industries was the first in America to manufacture a liquid hide glue some 80 years ago, and they sell it today under the name Titebond.  However they use ammonium rhodanate and dicyanodiamide as modifiers.  I was not happy with their product and when I used urea I found that the glue was much better in many ways.

Titebond glue does not need to be heated, and I think that is one of the problems.  OBG needs to be heated, by simply placing the bottle in a tub of hot water for a few minutes.  Hot liquid glue penetrates deeply into the cracks and pores of the wood and forms an amazing bond.  OBG actually works better than HHG for this reason.

OBG has a guaranteed shelf life of 18 months, and longer if refrigerated.  It can be frozen, heated and cooled as many cycles as you want without changing the quality of the glue.  It is common for me to reheat the glue dozens of times in a single working day.

You can find out more about HHG and OBG at my website www.OldBrownGlue.com.

Fish Glue

Fish Glue

For many years I purchased Colle De Poisson in Paris and brought it home for use.  I had a very unfortunate experience one time when the glue bottle and purple dye powder mixed together inside the luggage where my nice leather jacket was kept.  Everything would have been fine except the airline somehow drove a truck over my bag.  The worst part was when my wife found me at 2 am washing out my jacket in her bathtub.  That's another story...

Some time after that, as I was standing in the Paris supply house (H.M.B.) the owner asked me why I was buying fish glue.  He said it was silly, since the glue was made in North America by Norland Industries!  I stopped buying it there after that.  You can find it at Lee Valley or buy it from me.

Fish glue is normally liquid at room temperature.  We all used it in Kindergarten to glue paper together.  It was in a small glass jar with a rubber nipple top.  Some of the kids ate it.

Fish glue is used whenever wood is glued to something that is not wood, like leather, mother of pearl, ivory, brass, copper, bone, horn, tortoise shell, etc.  The reason is that fish glue has a very low sheer resistance and will allow surface materials to adjust to the wood movement during environmental changes without loosing adhesion.

Hide glues have a very high sheer resistance and will cause the wood to crack or the non wood materials to break free.

Thus, Fish glue is used for traditional Boulle materials.  The worst repairs I see on Boulle surfaces involve either nails or epoxy to hold down the surface.  That just makes it worse and my job more difficult.

Fish glue takes a long time to dry and can be easily cleaned up with cold water.  I would not use fish glue to make furniture or glue anything structural.

Rabbit Skin Glue

Rabbit Skin Glue

There are many other glues made from animal proteins.  The last one I will quickly mention is Rabbit Skin Glue.  This is diluted much more with water than HHG and used by gilders to apply gold leaf and gesso.

There is a lot more about glues to discuss.  Perhaps another time.  I will end this post and get back to work.  I hope this answers a few basic questions and serves to encourage others to explore the world of organic protein glues in their work.

You can find videos about working with these glues on our YouTube channel: 3815Utah.

There are also articles I've written which are posted on OldBrownGlue.com.  Note the article I wrote for SAPFM Journal Volume 2, "Why Not Period Glue?"  There is an excellent video on cooking and using HHG which was done years ago by Keith Cruickshank and posted on his WoodTrek's site.

Here is the video: Hot Hide Glue Video