Hi, I have been working with gum for several months and have gotten to the point that I can make a decent monochrome/duotone print but am not yet at the Tricolor level. What I am interested is if I am more or less right in how I percieve the relative importance of the printing variables. Since gum is a tricky process to learn, having a decent vision of what is going on can help to make it more predictable. I am using potassium dichromate and lana aquarelle cold press paper. I use compact fluorescent UV lamps to expose. I make digital negatives and apply Christina Z. Anderson's simple gum curve found in alternativephotography.com. I don't see the need to consider more sophisticated curves until I gain more skill with the process. The most important variable appears to be time as exposure time determines the ability of the gum to stick to the paper and the extent to which the highlights are colored. The second most important seems to be humidity. Here in North San Diego County, CA wild shifts in humidity can occur rapidly. I have to watch the National Weather Service and my hygrometer pretty carefully since humidity seems to dramatically affect printing times, and low humidity can make coating an awful experience. Below 40% I humidify my paper in a water based humidification chamber before coating and before exposure and I run a humidifier. This seems to bring a modicum of predictibilty to the exposure process (low humidity=long exposure-high humidity=short exposure. Pigment and pigment concentrations seem to be the third most important factor and since each pigment varies in how it bleeds out, tends to affect exposure and God(dess) knows what else, I ran some simple exposure time test strips and use them as a rough guide as I slowly get to know each pigment. Temperature of wash water and the ambient temperature seem to be the least important variables. There are variations with temperature and as summer approaches I expect to notice changes to the whole process. However if I were to compare temperature and humidity I would guess that humidity has a strong linear effect on the process while temperature has a weak linear effect. Anyhow those are the large factors I try to conceptualize and my way of thinking about them. I would be interested in any comments or suggestions for a better approach Thanks!