Old Brown Glue is hide glue that has been modified by adding urea. So it has all the qualities of hide glue but has a longer open time which you need if you are gluing on the top of a guitar or arranging braces. I only down side of this glue is clamp time it needs to be clamped for twelve hours and comes to complete hardness at 24. It does need to be warmed in warm water to use it. I am excited about this and I would recommend it even to a beginner because if you make a mistake you can get it apart without destroying the wood. I have used many kinds of glue and they all have pluses and minuses but this it what I use now. If you are using this repairing old furniture hide glue is the only glue that will stick to itself which is a big plus. Tim McKnight the luthier did a test on glue hardness which can be found on the internet which sites hide glue as the hardest. Many believe the harder the glue the better the sonic transfer for musical instruments.