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Hide Glue: Furniture found in the tombs of Egyptian Pharaohs shows that hide glue has been used as an adhesive for over 3500 years. Until the invention of Aliphatic resin glues in the early 20th century, hide glue was the standard adhesive for producing furniture, musical instruments and many other products.

Original formula hide glue is still produced today and remains the choice of professional craftspeople for repair and restoration of antique furniture, clocks, musical instruments and numerous other high-quality applications.

Much has been written about the virtues of hide glue in clock case repair and restoration. Craig Burgess of NAWCC chapter 124 has an excellent dissertation on the advantages of hide glue in his message-board posting Hide Glue 101 .
A special thanks to Craig for taking the time to review this presentation and offer his suggestions for additions,
clarifications and corrections.

Some of the key advantages noted for hide glue include:

  - Hide glue is a reversible process. Glued joints can be disassembled without damage to the base wood and
    glue residue can be completely removed from wood pores. This is particularly important in restoration work
    where you (or someone 100 years from now) may need to disassemble a wood joint or remove a section of
    veneer. This is a simple process with hide glue that just isn't possible with modern glues.

  - Hot hide glue quickly assumes a "tack". This greatly speeds assembly and eliminates much of the need for
    clamping and pressing. Two wood pieces can be brushed with hide glue, held tightly together for a short
    while and the glue will quickly take over.

  - Newly applied hide glue is compatible with existing (old) hide glue. This is very important in restoration
    work where new and old elements are often used side by side.

  -  Compatible with wood stains. When modern glue touches raw wood, the pores are filled and the glue
     cannot be removed. As a result, wood stains cannot penetrate evenly. This is the reason for "blotchy"
     inconsistent stain finish often seen on wood projects assembled with modern glue.
     Hide glue, on the other hand, is water soluble and can be completely removed using a damp cloth or
     toothbrush. Once the hide glue is removed, wood stain will penetrate the wood uniformly.

The following presentation illustrates the basics for getting set up and started in the use of traditional hot hide glue.
 


Hide glue is derived from "collagen" which is a protein constituent of animal hides, bone and connective tissues associated with the hides.

Raw materials originate in the meat packing and tanning industries and are primarily of bovine origin.

Hide glue is graded in terms of "gram strength". 85, 108, 135, 164 192, 222 ,251, 283, 315, 347, & 379. The higher the gram strength, the quicker the set. Generally #251 gram strength is recommended for woodworking.
 


Hide glue is available in two forms: 

   - Premixed (liquid)
   - Dry granules .
                      


Premixed (liquid) hide glue was first produced by Franklin International in 1935. Franklin still produces it today under the brand name "Titebond".

High quality, custom blended, liquid hide glue is also available from woodworker/conservator Patrick Edwards

While premixed hide glue is convenient, one important drawback must be noted: Shelf life. The expiration date is stamped on every bottle of Titebond hide glue. It should never be used beyond this date.

Unless you are doing a good bit of restoration, the expiration issue can result in quite a bit of wasted glue.


The traditional form of hide glue is dry granules that are mixed with water to reconstitute.

There are a number of retailers of dry hide glue, but the source for almost all hide glue in the U.S. is Bjorn Industries in North Carolina.

Milligan & Higgins  is also a large supplier of granular hide glue in a number of different strength formulations.

The shelf life of hide glue granules is basically indefinite if kept dry and cool.

Once mixed, the shelf life of hide glue is quite short (2~3 weeks). There are ways to significantly extend the shelf life of mixed hide glue. This will be detailed later in this presentation.
 


 

Hide glue can also be purchased in the form of "Pearls" from sources
such as Woodworkers Supply but granular hide glue is considered a
purer grade is generally easier to work with.

 


Mixing Hide Glue: The normal mixing ratio is one part hide glue granules to one part water (both by volume). The granules should be allowed to absorb water for about 10 minutes then the mixture can be heated to completely dissolve the remaining granules.

If using hide glue "pearls" the water/pearl mixture should be allowed
to sit over night to allow the pearls to absorb water and soften.

Hide glue made from granules or pearls is normally heated and
applied "hot" but can be made into a "liquid-at-room-temperature"
form by adding 5 table spoons of urea (or 3 tablespoons of salt) for each cup of dry glue.

This presentation will only cover the use of traditional "hot" hide glue.
 


Heating Hide Glue: Hide glue must be warmed and maintained at a consistent temperature. It should not allowed to boil or "cook" as this will significantly reduce the bonding strength. A maximum temperature of around 140 degrees F is normally used.

Special "Glue Pots" are available from many woodworking suppliers and work well for maintaining consistent, safe temperatures. Unfortunately, these units are relatively expensive costing around $125.00.

Unless you do a lot of glue work, this is a difficult investment to justify.
 


A fully functional "Glue Pot" can be easily made for under $20.00 using an electric "kettle" such at the one shown. This unit was purchased at Target for $9.95 in 2006.
 


 

A glass jelly jar or baby bottle is used to suspend the glue in a warm water bath and maintain a safe, consistent temperature.

 

 

 

 

After adding enough water to the kettle to cover the sides of the
glass jar, the kettle is turned on and the water heated.

A meat thermometer is used to monitor the temperature of the water.
The thermometer can also be placed into the glue for a direct
temperature reading.

Remember: Do not allow the hide glue to be heated above 140 degrees. Overheating will damage the glue and reduce its strength.

As shown the kettle, thermometer and bottle cost well less than $20.00 and do an excellent job of maintaining the correct glue temperature.


 

Once the correct setting for the knob on the kettle is determined it should be permanently marked.
 


 

When heating the glue, a lid should be placed loosely on the jar  to prevent excess evaporation and keep the "smell" down.
 


 

Applying Hide Glue: A stiff bristled brush such as an acid brush is normally used to apply hot glue to both surfaces to be bonded.
 

 

 

 

 

Brush glue onto both surfaces.  There is no advantage to applying
excess glue, but there should be enough that a small amount of "squeeze-out" is seen when the two surfaces are pressed together.


 

The freshly glued joint can usually be held together for a few moments
and the hide glue will cool and quickly become tacky.

 

 

 


The quick setting property of hot hide glue is a big advantage
in assembly since less clamping is usually necessary to keep pieces
aligned and tight.

Any excess hide glue squeezed from the joint can be wiped away with
a damp cloth. If cleaned well, the wood will accept stain normally.
Modern glues cannot offer this advantage.

Once the glue "gels" the joint should be left undisturbed for several
hours as the glue dries.



EXTENDING THE WORKING TIME:
The quick-setting property of hot hide glue is not always an advantage. For example, when applying veneer to a large panel. In a case such as this a longer "open"
time is very beneficial.

The "open" or working time of the hide glue can be extended by thinning the glue slightly with water or by heating the working surfaces.
An infrared household heat lamp (250W) can be used for this purpose.
 


STORING HIDE GLUE: As noted, dry hide glue granules can be stored indefinitely in a cool, dry place.

A sealable food storage container works well to keep moisture out.

Mixed hide glue, on the other hand, normally has a useful shelf life of only a few weeks.
 


To avoid waste and the need to mix a new batch of glue every time you have a small glue job, hide glue can be mixed in larger-than-needed quantities and preserved for future use by "freezing".
 


 

Any unused hide glue is simply poured into an old ice tray and
allowed to cool and gel.

It can then be placed in the freezer to preserve it until needed.

 

 

 

Once frozen hard, you can leave it in the ice tray or remove the
"Glue-cubes" and wrap them in foil, and place in a freezer bag.
This is usually more acceptable to other members of the household.


The advantage of mixing and freezing small cubes of hide glue is that
the needed quantity of ready-mixed hide glue can simply be removed
from the freezer, dropped into the glue pot and allowed to heat up.

This makes using authentic, traditional hot-hide-glue as convenient as using any other type of glue, but with the advantages only hide glue
can offer.

Note: Once thawed, hide glue should not be re-frozen. It can be heated for use, allowed to cool then re-heated as with hide glue that had never been frozen. However, remember that hide glue is an organic compound and will eventually "spoil". After a few weeks of heating and cooling it is best to discard the residual glue and start with fresh. 
 


That pretty well covers the basics of getting set up to use traditional hot hide glue. If you have never used this product
you owe it to yourself (and future collectors) to give it a try. You're in for quite a surprise when you see how easy it is
to get set up and how well hot hide glue works on your clock case projects.

Regards,
Tom Temple