This section is from the book "Modern Photography In Theory And Practice", by By Henry G. Abbott. Also available from Amazon: Modern photography in theory and practice: A hand book for the amateur.
The formula gives sixty ounces of water and three to five drams platinum solution. Of course, it depends on how many prints there are to tone. So the best formula to follow will be to place enough water in the tray you expect to use and add about three drams of platinum solution to start on. The speed of this bath should be from eight to fifteen minutes. If necessary add more platinum until you get it, for it is platinum and not water that tones. A print slightly toned in the gold bath will take more time and platinum to tone in the platinum bath. If a print be left very warm in the gold bath and toned hard in a strong platinum bath, it will be a strong olive, as overtoning with platinum gives greenish or olive-black. If you tone to purple and deposit a good lot of gold on the print, it takes less platinum and time to tone and will remain a pure black. Too slow toning in the platinum bath flattens the whites and has a tendency to muddy the shadows. The platinum bath is very acid. Only use one-half to two-thirds old bath over. If you use all the old bath over and all the acid is left in the old bath and you keep adding fresh platinum solution, you will get it too acid and are in danger of cutting out your prints.
In making up the hypo bath, always use the hydrometer to test it. For Junior and Blue Label use fifteen grains hypo and fix fifteen minutes. For Platino paper, use eighteen grains hypo bath. If you wish to fix Junior and Platino together, make the hypo bath fifteen grains strong and fix fifteen minutes. A thoroughly fixed print is easily washed; but too long fixing is as bad as too little, as it bleaches your prints and destroys their brilliancy.