HIDE GLUE
(JOINERS PEARL GLUE)
 

The following is an extract from... 
A Polishers Handbook, written by Neil Ellis

HIDE GLUE

Most modern glues are not able to re-bond to other glues or for that matter to themselves so clean timber to timber contact is a must, especially when working on the restoration of furniture.

Hide glue on the other hand will reglue to old hide glue and form a good strong bond to boot. This doesn't mean that you need not clean out the joint before reglueing, but you do not have to put in quite as much work as the old glue can be mostly removed with hot water and a rag without damage to the joint. The new glue will then bond to the residue that remains in the joint and is already keyed into the timber.

Hide glue comes in a powder or pearl form and is mixed weight for weight with water. ie 100grams of powder is mixed with 100grams of water. (I prefer to use rain water) This is left to soak for a short time, it will shell up during this time as the glue soaks up the water. It is then heated in a double boiler until it melts and kept at a constant temperature around 80 degrees Celsius. The glue should resemble a thick broth when it is ready for use.

Paint the glue on to both joints and press them together using a clamp. The new glue will melt the old remaining glue in the joint and form a new bond. You will have to work fairly quickly as the glue sets or rather jells very fast, especially in cold weather. The setting time can be retarded with the addition of a little extra water or by warming the joint prior to applying the glue.

Another plus for hide glue is its speed in setting. Because it works so fast it is some times not necessary to use clamps to hold a piece. In some instances you will find the addition of glue blocks to the back of a joint will strengthen and hold the piece together making for an easier and stronger repair.

Glue blocks are small pieces of timber usually triangle shaped. These are used to lend extra support to a joint especially on corner joints. Glue is painted on the two right angled faces, the block is placed in position and then slowly but firmly rubbed up and down until the glue starts to grab and the block can no longer be moved freely. These blocks have many applications in restoration work.

MORE ON HIDE GLUE
This type of glue is still reasonably easy to get though you may have to send for it by mail. I keep a supply of it on hand at the school for students use and for sale. See add & suppliers list at end of book.

The two main types of hide glue are:
Pearl glue - small hard beads which should be soaked for a little while in their own weight of water before being heated. This is the recommended type to buy.

Powder glue - is a powdered form of the above. Harder to get mainly sold in art supplies shops as rabbit skin glue.

Hide glue, as the name suggests is an animal bi-product. Basically it is a gelatine made from the processed hides and bones of animals. Recycled horse and cow etc. It has one minor flaw and that is the fact that it has a rather distinctive odour which is not very pleasing to the nose. (It stinks)

HEATING THE GLUE
Before hide glue can be used it must be heated to around 80^oC, this is traditionally done in a glue pot which is in fact a double boiler. Electric versions of these are available today with thermostatic control. They are however rather expensive (well in excess of $100). There are alternatives. I purchased a second-hand, thermostatic controlled, electric baby-bottle warmer for $4 from a Trash & Treasure Market. This is just the right size to hold an empty 100gm glass coffee jar. This jar in turn will hold enough glue to do a rather large gluing up job.

If I need to do a lot of gluing, eg. to veneer a table top or a complete set of dining chairs etc. I would use my large glue pot. You can make something similar by using a plastic honey bucket and suspending it inside a large Ovaltine or similar tin, cut a hole in the lid of the honey bucket and put your glue brush through it, this will help to stop the glue from drying out and skinning on the top.

Diagram shows a honey bucket suspended in an Ovaltine tin.

To melt the glue in your makeshift glue pot pour boiling water into the tin then put the bucket containing the glue in and stir the glue constantly for about 5 minutes or until it has all become liquid. The glue should then be at about 80^oC and ready for use. Alternatively you can place the tin into an electric frying-pan which has an inch (25mm) or so water in the bottom and keep it at approximately 80^OC for a longer period of time.

GESSO
Hide glue can also be mixed with talc or calcium carbonate (chalk powder) to make gesso. This is traditionally used as a base upon which to apply gold leaf, however it can also be used in a number of decorative finishes as well as a grain filler on open grained timbers.
See the page on Talc