One of the most time consuming and painstaking tasks associated with piano restoration, ivory repair rates up there as one of the most difficult to accomplish properly.
The removal of old broken or chipped ivory is fairly easy and straight forward to complete. The original ivory glue is heat and water activated so heat and water make it soft once again.
I have found over years of practice that for most ivory repairs it is a waste of time to try to match existing pieces with another head or tail. If one side of the ivory, either the head or tail, is missing or chipped, I have found it best to replace both pieces. When replacing both pieces the difficulty of matching the seam between the head and tail of different qualities of ivory does not present itself as a problem.
Here are two of the most common ways to repair ivory; first using the pre-glued linen wafers, and then using the original premixed hide glue readily available from suppliers in Germany.
Unless ivory repairs are done all the time one gets out of practice immediately.
At times, with certain manufacturers, ivory pieces can be retrofitted from one head or tail to another but very few companies had a continual supply of ivory that was identical in grade and quality. With the Heintzman Company of Canada the quality of the ivory was quite consistent so I am able to replace a chipped head only in this case.
Whether replacing just the head or doing the complete head and tail assembly, I have found it best to set the head first. This is to obtain the correct length over the leading edge of the key. Here is a photo album of setting an ivory head against an existing tail with text instructions underneath each photo.