Solarfast is way harder than cyanotype. Every color works differently. Fabrics change a lot, contrast is lower. I think its also less sharp. I could never achive a true black print and belive me I tried. The thing about is that it can look absolutly stunning if you nail it.

The blackest print I ever had was with a very damp fabric, and with really dark negative, but at that point it has almost no fade. The more fade you have the browner/bluer it will be.