Saturday, May 14, 2011

Animal Protein Glue

I have never had any difficulty speaking in front of an audience. I have given hundreds of hours of lectures, as well as quite a bit of television. Generally, I speak about Decorative Arts, focusing on antique furniture issues. Quite often, when I speak about living and conserving wood furniture, I am asked, "How do I find a good craftsman to repair my antiques?" I usually respond like this: "Ask the prospective restorer if they have a glue pot, and what kind of glue and finish they use."

It has been my experience over 40 years that, if the woodworker uses protein glue, shellac and wax, he understands antiques. It is essential that reversible methods and materials be used in restoration, and that the glue and finish selection is as close to the original as possible. Using modern adhesives and finishes will negatively affect or completely destroy the value of the object. All furniture is subject to damage, either by wood movement or actual use or abuse over time. Therefore, the repairs need to be reversible.

I have never missed a chance to promote or discuss the virtues of animal protein glues during my career. For example, when the Society of American Period Furniture Makers organized, I quickly joined the group and began contributing to their Journal, which has evolved over the past decade to become a great source of furniture making research. In January, 2002 (Volume 2) I contributed an article, "Why Not Period Glue?" The inspiration for that article was that, after attending two SAPFM conferences at Williamsburg, I realized that the members of this group were very concerned about early furniture, construction methods, using antique tools, and even shellac finishing. The one thing I noted in talking with many members was that they generally used modern synthetic adhesives without even thinking about it. So, I raised the obvious question in my article.

Later, in March 2008, I wrote an article, "Hide Glue" in Fine Woodworking (Issue #197), which attempted to reach a much larger audience. This followed the feature story, "How Strong is Your Glue?" (Fine Woodworking #192, August 2007), where both hot protein glue and my Old Brown Glue were tested in objective and scientific conditions. I also made a video with WoodTreks, which discusses the preparation and uses of this glue.

Traditional animal protein glues have been used in all cultures for thousands of years. The protein is organic, easy to cook and adaptable with many diverse types of additives. There are quite a few different sources of protein, and each produces a different type of glue characteristic. Rabbit, fish, animal bone, hide, blood and other materials all have been used for making glue. In America, generally starting after the first World War, synthetic glues were developed and introduced, which quickly replaced the traditional glue pot in the workshop. Other countries continue to use old fashioned protein glues even today.

There are many misconceptions about using animal protein glues, which I address in my published articles. I believe that these beliefs are a result of authors who do not have direct experience with the material, and simply include in their writing "facts" which were previously published by other authors with little experience. Statements like "It smells bad," or "It goes bad quickly," or "Make only what you need at one time," or "It is not as strong as modern glue," or "It is difficult to use," are false.

I have posted a chart here which I use in my class to explain the simple properties of this glue. There are only two factors to consider when working with this glue: heat and water. If there is any problem at all, just figure out which of these two factors needs to be adjusted to fix the problem. Either add or subtract water or raise or lower the temperature. Or both.

You will note from the chart that both of these factors combine to determine the viscosity. Think of water, for example. It is either solid (ice), liquid or air. It can change from one state to another and back again, over and over, simply as a question of temperature. Animal protein glue is the same, It is either solid, gel or liquid, also as a function of temperature, with the addition or removal of water as a second important factor. More importantly, this glue has the property of changing from one state to another, again and agin, without damage. This is what makes it reversible.

It is important to understand that you must add cold water to the dry glue to fully hydrate it before adding heat. If the glue is a solid slab, the way it is sold in Europe, it must be broken up into chunks and soaked overnight. If the glue is granulated, or in pearl form, it hydrates much quicker. You will know when it is hydrated since it turns into a thick gel. Then you need to put it into a double boiler and raise the temperature to 140 degrees to use it.

I don't have the time here today to discuss all the features of this hot glue. Read my articles, some of which are posted on and let me know if you have any questions. Get some glue and play with it.

I want to discuss briefly how I came to make Old Brown Glue, which has enjoyed increasing success in recent years. I was fascinated by how early 19th century cabinetmakers were able to veneer columns. For years I tried, without success, to do the same using hot glue. Then, about 20 years ago I joined an international group in Paris which focused on marquetry conservation issues, including modifying protein glues to do a specific job.

That experience led me to do my own research on using urea to reduce the gel point of hot glue. I cooked 37 different batches to test the recipe and finally succeeded in a formula which did what I wanted it to do. Essentially, the urea attaches to the Hydrogen bonding sites and thus reduces the temperature at which the liquid glue turns to gel. Since urea and protein collagen are natural, organic materials, this glue is non toxic in nature.

After perfecting the recipe, I was able to veneer columns without problems and you can read about this technique in Fine Woodworking (Issue #173) December 2004. The Master Class article, "Low-tech method for veneering columns," featured a desk I made on the back cover of the magazine.

I start with 192 gram granulated protein glue made by Milligan and Higgins. I cook it in the bathroom at the shop, add the urea and the "secret" ingredient and put it into bottles. It takes some time, and I will never get rich doing it, but I am pleased that the demand is such that I need to cook a batch every other week.

Old Brown Glue has a shelf life. We put a date of 8 months on the bottle, and each bottle has the batch number on the top. I am currently shipping batch 150. It can be kept in the refrigerator and will remain good for over a year. It needs to be warmed up to use it, and I just place the bottle in a pan of hot tap water when I use it. You can heat and cool it as many times as you want, just don't dilute it.

There are three indicators that the Old Brown Glue has gone bad: 1) It has a very liquid viscosity at room temperature (it should be a gel in the bottle), 2) It smells strongly of ammonia, and 3) It has mold visible inside the bottle. If a bottle is past the date on the label, please take the time to do a test before you use it on your project.


Steve R said...

Thanks for posting.

I have been using hot hide glue for a couple of years but only on things I know i can get under clamps quickly.

My next step is working on additives to extend the open time for bigger glue-ups.

This post is timely.

Can you help with a good source for urea?


W. Patrick Edwards said...

As you work with animal protein glue, you will gain the experience to use it without problems. Remember, the cabinetmakers working in New England, during the winter, were able to make magnificent furniture, using only protein glues.

Urea is one of the additives that lower the gel point, but there are limits to how much you can add.

I use pure urea, in the form of small white pellets, which I purchase from the local chemical supply house. Urea is not expensive, and is commonly used as a fertilizer.

Practice, practice, practice...

Steve R said...

Is there evidence that they used additives historically or did they just deal with the open times by managing the temperature of the room and work?


W. Patrick Edwards said...

I have researched several early 19th century references which discuss the varieties of additives that can modify different protein based glues. The early craftsmen and artisans were much closer to the sources of their materials and had a more direct control over their preparation and use than we do.

That said, of course workshop environment conditions and material preparation has always been essential for success. However, the first indications I have of a company relying on the elevated temperature of the workspace is the shop of Belter, in New York, working in the 1850's or Thonet, in Austria, also during the same time. Both of these shops produced steam bent and laminated materials using protein glues. This was new technology at the time and required a much more sophisticated process than the Yankee cabinetmaker holding his table top in front of the stove in winter before veneering it.

Good question.

Anonymous said...

Hi Patrick

I did try to add sea salt to my hot hide glue with little success. My guess is that the proportions were not good.

any recommendation on this?



W. Patrick Edwards said...

In general, it is not practical to just add something directly to the hot glue pot to modify its properties. In formulating a glue, you really need to add the modifiers during the initial mixing stage to get consistent results.

When I started experimenting with OBG I threw out 37 batches of glue before I reached the proper formula. Then, at batch 104, I made a slight adjustment to the mix and achieved the perfect results. That process took several years of work.

I have a background in physics and chemistry, and a basic understanding of French. I purchased a book in Paris which gave me a good insight into glues: "Traite General de la Fabrication des Colles" published in 1959 by Dr. Maurice De Keghel. I do not know of any English version, but you may search online for references on modifying animal protein glues.

My observation is that salt is not very effective as an additive as it has a weak effect on the molecule. Urea bonds very effectively with the Hydrogen atoms and directly affects the gel point.

Keep your hot glue pot for hammer veneering, rubbed joints and quick set repairs, and just buy Old Brown Glue for all other woodworking. Leave the cooking to me.