The standard solution sold is 42° Baume. Baume is specific gravity, not % solution. 42°Baume is around 38-40% solution in FC. Other liquids with different densities have different %vs°Baume. For example, 42° Baume nitric acid is 67-68%.
42° Baume FC is diluted 1:3 with water to make the standard etchant for steel blades.
Here is one of my old posts on mixing FC from powde:
Mix it outside and stay upwind. It gives off a chlorine gas when you first mix it. It also can get very hot while mixing. Add the powder slowly to the water. Don't mix it in a thin plastic jug ( milk jug)...it might melt. Mix it in a heavy plastic bucket, like a drywall bucket. When cooled down, pour into a plastic storage container and wash out the mix pot.
FC should be mixed to make a 42 Baume stock solution. You add one pound of crystals to 18 ounces of water to get this strength - one pound to one pint is close enough ( four pounds to a gallon). Distilled water us best, but any water that is not full of minerals (I use bottled water) is fine. Let it sit for a couple days before using it. Dilute the working solution from this stock . Three parts water to one part stock is what most folks use.
If you are just making up one gallon, skip the stock solution, and add one pound FC powder to a gallon of water. If making up a larger batch, one gallon of stock solution is easier to store than four gallons of working solution.
Again - Mix outdoors and don't breath the fumes when it is dissolving. Wearing gloves and a face shield, is a good practice.
