John Whiteside replies: There is not a fixed open time for hide glue. For thickly mixed hide glue applied to a cold joint, the open time is less than a minute. For thinly mixed hide glue applied to a joint that is kept at a temperature above 140 degrees, the open time is, for all practical purposes, infinite.
This means that the woodworker can extend open time by making the glue more dilute and by heating the joint. Dilution is achieved by adding water and observing how easily the glue drips off the glue brush. Heating the joint can be accomplished by using a hair dryer, a heating pad, an infrared lamp, or simply by raising the temperature in the shop.
In practice, with the right dilution and joint temperature, you can achieve open times of several minutes. Of course, if the hide glue sets prematurely, it can simply be released again with moist heat, That’s the huge advantage of hide glue—it is reversible.
Al Breed replies: The 192 gram strength (maybe it’s 92?) hide glue that I use sets up quickly. With this glue from the glue pot, you don’t have any open time at all if the surfaces you are gluing are cold. If it gels when it hits the wood, it won’t hold. I warm the surfaces up with a heat gun to give myself some time to work because warm surfaces equal longer time as a liquid for the glue, which gives it time to penetrate before it sets up. It takes some time to get used to using hot glue. Some different gram strengths do have different open times, but my advice to students is don’t take your time.