Now this is by no means a scientific test, but it was inspired by one done on another forum with hot hide glue. So I quickly prepared a sample by gluing two pieces of wood together in an end grain to face grain butt joint. After it dried for 48 hours (the weekend), I placed it on the ground like this.
I then stomped on the apex of the joint and the result was:
As you can see there was better than 70% failure of substrate (wood broke) and the rest failure of adhesive. This test differs slightly from the other test in that I did not size the end grain of the wood prior to gluing. I have another sample in clamp as we speak and this one is sized, so we will see if there is any improvement.
Still this is quite impressive as was the test with hot hide glue. The wood here is Eastern White Pine for both pieces.
There was some discussion about additives to hot hide glue lowers its strength. Those additives in question are anti gelling agents or gel suppressants (same thing), and any addition to hot hide glue will effect its strength. Hot hide glue is just stronger than liquid hide glue. But the difference is not that much, look the wood failed.
Other additives like filler to improve gap filling and aid in production can be added up to 10% without diminishing the holding capabilities of either hot or liquid hide glue. Adding small amounts of pigment such as whiting to change the color of the glue has little effect on the strength, up to the 10% limit. After that the strength does begin to diminish as the percentage of additives increase. When it comes to liquid hide glue the anti gelling agents do continue to effect the protein bonds of the hydralized collagen (hide glue), effecting the viscosity and strength over time.
Keeping liquid hide glue refrigerated or frozen will slow down the chemical process but there comes a point when the glue fails the legging freshness test and is religated to crackled finishes or thinned out and used in the garden. If you use hide glue as your regular glue then the expiration issue is not a problem.
Hot hide glue is stronger than liquid hide glue when both are properly applied. But liquid hide glue is still plenty strong enough, the difference is measureable but I don’t think significant for normal woodworking applications. I have no problem using liquid hide glue on any furniture I make, including chairs. When the shop is warm I do break out my charcoal brazier and heat up the glue pot, in the summer the warm weather lends itself to hot hide gluing. The warmer the more open time.
It is interesting that the warmer the temperature the shorter the open time of liquid hide glue.