My platinum process is dispenses with 19th century paper hydration, heavy breathing, and ridiculously dangerous antics such as blowing a hair dryer across paper sensitized with oxalates, metal salts, possibly even dichromates, and instead uses ascorbic acid (vitamin C) to trigger the image-forming reduction of platinum on dry paper. It's simple, direct, cost-effective, and cheaper than palladium now that palladium chloride has shot up from around $500 and ounce to nearly $1500 an ounce.
Contrast control is basically mixing fewer or more drops of C with a solution of sodium ferric oxalate or ammonium ferric oxalate or using Richard Sullivan's excellent lithium ferric oxalate for its strong contrast boost as compared to the other two double ferric oxalates. For the OCD types hell bent on printing out those negatives they exposed 40 years ago for printing straight on Grade 2 silver gelatin paper, 26% ferric oxalate with no C added, can bring a strong contrast boost without the introduction of horrifyingly poisonous and carcinogenic dichromates.
1. Dissolve 1 gram of platinum chloride in 5 ml of distilled water.
2. Prepare a 37% solution of sodium ferric oxalate (sodium carbonate, oxalic acid, ferric oxalate).
NOTE: You can substitute 40% ammonium ferric oxalate as Pizzighelli specified in his mostly forgotten 1890 formula for print out of platinum on hydrated paper (see the Mike Ware instructions for printing platinum for Pizzighelli's process; it's essentially the same as the Malde-Ware "discovery" [in an old book at the British Museum...]).
3. Prepare a 2% solution of vitamin C, ascorbic acid.
4. Count 8 drops of the 2%C into the bottle containing 10 ml of either sodium ferric oxalate or ammonium ferric oxalate.
5. Shake the bottle vigorously.
(Note: if the above instructions are too complicated, there is a forum on the internet, Photrio-Analog, for you and your ilk.)
6. Mix the sodium ferric ferrous oxalate (or ammonium ferric ferrous oxalate) 1:1 with the platinum chloride. The typical volume for an 8x10 print is 12 to 16 drops of sodium ferric ferrous oxalate and the same number of drops of platinum chloride.
NOTE: Before mixing the two, count the platinum chloride drops into a shot glass. Freeze the platinum solid, then thaw it in a tray of hot water. Swirl to redissolve the platinum. Then refreeze the platinum (a second time) and thaw it a second time. This freeze/thaw procedure is only necessary for about 21 days after you first prepare the platinum solution. Thereafter, you can mix the platinum chloride with the double ferric ferrous oxalate without freezing/thawing.
7. Add half as many drops of glycerin as of platinum chloride (such as, 7 drops of glycerin to to 7 drops of platinum).
8. Swirl to mix all the solution components, then pour onto a sheet of paper such as Bergger Cot 320/160, Hahnemuhle Platinum, or Legion's Revere Platinum.
9. Once the sensitized paper is DRY (wait for it), place a sheet of 2ml or 3 ml mylar on the paper, then place your negative emulsion side down in contact with the mylar.
10. Mount the sandwich in a contact print frame and expose it, by examination, until the final image is approximately 1/3 stop lighter than the desired final.
11. Clear in weak (1% or so) muriatic acid for 15 minutes. Then wash in running water for 5, then clear in 10% tetrasodium edta for 15 minutes, then wash in running water for 5, then clear in the tetrasodium edta for 15 minutes again, then wash in running water for 30 minutes.
Unlike the Pizzighelli process, re-announced in 1986 by the Scottish university don and a Tanazanian photographer, this process requires no palladium, and leaves behind the 19th century mindset for a 21st century approach to printing platinum. It is utterly reliable and prints out a beautiful photograph in pure platinum every time.