I've never fixed a print after toning in my life but I generally only use Selenium, Tetenal Gold and Sepia. I've no experience with Nelson's gold and would take Ann's advice if you plan to use it.
Originally Posted by FrankB
If you are planning to split sepia and fully bleach you are likely to loose the highlights depending on which paper you use. Try this tip; mix a very weak solution of the bleach,1 to 30 or 40 is a good starting point. Bleach the print for about 20 seconds, you need to experiment with this for it depends on the tonality of the highlight mine are just on the paper. Remove the print and wash then tone it in the toning solution, 5 minutes will do. You will see no significant change in the print other than the highlights will have been slightly bleached and then sepia toned. Wash the print again and place in a full strength bleach and leave until it's bleached to the degree you wish. The highlights will not have bleached any further than they were after the first bleach. Wash yet again and place in the toner until it's the colour you want, remove and wash for the final time.
The reason for the first bleach it simply to enable you to hold the highlight just where you printed it in the first place and the bleach converts the silver halides so that they cannot be affected by the second bleach.
When split sepia toning the degree of bleaching will have a significant effect on the outcome so do experiment with how much bleaching you apply.