Negatives for gum, particularly single gum, should have a limited contrast range of about 0.7 (such as you would choose to enlarge on harder paper), or otherwise you are likely to get empty highlights or shadows.
Originally Posted by argus
Single gum is quite different from multiple gum, in aesthetics as well as in the technique. Don't think it is easier. I once had the opportunity to inspect original prints by Robert Demachy in Paris (single gum prints) which had an absoulutely intriguing tonal range and quality, and I must confess I would not be able to make them. Single gum prints in my experience have the tendency to either lack density in the shadows / maximum density, or to become harsh, or both. But if you get everything right...
You most probably will not want additional sizing with single gum, at least not if you are looking for fine highlight tones, but it will be essential - or near essential - with multiple gum to prevent staining. You can print down larger contrast ranges by first printing the highlights and then the shadows, and it is much easier to get the shadows right. You can use multiple colours. It is, of course, time-consuming, and you need a technique of re-registration. This problem increases with the size of your prints. Contrast can also be separately influenced in every layer you coat.