Warmtone RC tones well in most toners having been designed for that purpose. I have no experience of Paterson Selenium Toner but my prediction is that it will not be as strong as Kodak which IMO is the best selenium available. Therefore you will have to adjust the dilution if you are making comparisions with other brands.
I use Fotospeed selenium for it is a good compromise when cost and strength are taken into account. My usual dilution is 1 part toner to 9 parts water at a temperature of 24 degrees c. although I do sometimes use it at 1 to 4 at very high temperatures when I'm looking for extreme effects but do be careful if you do this for the fumes are extremely unpleasant.
If you have never toned before I would suggest that you make a number of identical prints, place them in a holding tray of water and tone them in turn for different times. Don't keep looking at the print being toned for you may find it difficult to see the change in colour, compare the toning print to the untoned print in the water to help detect the changes.
As a general rule selenium will affect the lower values first so you should see those areas getting darker first followed by the other tonal values and ending with the highlights being the final area to be affected. Having said that, once toning starts it can happen very quickly. I don't subscribe to the view that you can tone every print for a standard time for toning depends on the tonality of the print as I stated above, therefore how can a high key print tone as quickly as a low key print.
You must learn to anticipate the effect of the toning so that you can remove the print from the toner and place it into a tray of plain water to stop the action. After toning you need to wash the prints before drying, 5 minutes in running water is more that sufficient for RC paper.
Please take this advice as a starting point, what pleases me may not please you for this is a very subjective matter. Have fun and keep us posted as to your progress.
