Here's an excerpt from my gum printing workshop manual:
Originally Posted by shinn
"I have only ever used one type of gum arabic. It is the spray-dried powder available from Bostick and Sullivan. Gum arabic can vary widely from manufacturer to manufacturer and from one year to the next. The B&S gum has been very consistent and works very well. You can buy it in solution, or mix it yourself from the powder as follows:
Add 300 gm powder to 1000 ml of water. Stir vigorously until the gum is mixed as much as possible. There will probably be quite a bit of stuff floating on the surface, but that will mix in eventually. Place the container (covered) in the refrigerator for several days and stir it several times a day, mixing in any lumps that may be present. After a few days, there will probably be a little bit of foam on top, which you can just skim off. To preserve the gum solution, add 3 ml of 1% sodium benzoate per liter. Place the gum solution in a plastic bottle so you can squeeze out any air in the bottle when you seal it. The gum does not need to stay in the refrigerator once ready for use."
I've never determined it's Baume rating, but I know that it works very, very well.