Dante I'm not sure if ready-made (designed for S/G printing) gold-thiourea toner is OK. I have always used the toner mentioned here:

http://unblinkingeye.com/Articles/Vandyke/vandyke.html

Regards,
Loris.

P.S. BTW, I use anyhdrous KAuCl4 instead of the usual gold chloride compound and it works OK.

See the excerpt below:

"...

Clerc's Thiourea Gold Toner

The solution requires no aging; it is ready for use directly after mixing. It tones highlights and shadows at the same rate so the print tones evenly and can be removed from the toning bath at any time. It keeps well and resists decomposition even after moderate use.

Formula

Gold Chloride (1% solution) 12.5 ml
Thiourea (1% solution) 12.5 ml
Tartaric Acid 0.12 gm
Distilled Water to make 250.0 ml
Sodium Chloride 5.0 gm

Compounding

Make up a 1% stock solution of gold chloride by dissolving one gram of gold chloride (AuCl3HClH2O) in 100 ml of distilled water. Keep the solution in a brown bottle. Likewise, make up a 1% stock solution of thiourea. Uncontaminated, these solutions keep indefinitely. Add the thiourea solution to the 12.5 ml of gold chloride solution until the precipitate that forms is dissolved. The quantity of the thiourea solution should be slightly more than that of the gold chloride. Add the tartaric acid to 150 ml of distilled water. Add the gold thiourea solution to the acid solution and mix thoroughly. Last, add the salt, top off with water to 250 ml and stir until the solution is uniform. Bottle and label the solution.

Toning

Make sure that the tray and tongs that you use are clean. Immerse the the developed, cleared, and rinsed print quickly into the toning bath (or pour the toner onto the print). Agitate the print frequently during the toning period--five to ten minutes, depending on the condition of the toner. After toning proceeds to a satisfactory color, rinse and fix the print. Finally, wash the print for 20 minutes.

..."