For this variety of Cortinarius I used the entire mushroom, not just the caps, because color can be found in the stipe and the caps. I tried both an alkaline dye bath pH9 and an acidic dye bath pH4 and the results were the exact same. I expected some variation and my recommendation is to work with an acidic dye bath using vinegar as it is just a bit easier. However, I was blown away by the pigment when I modified the paint with sodium carbonate, it immediately turned a deep, autumnal red. I was lucky to have these gifted to me by my friend Michael as Cortinarius californicus is unique to California.
I met Michael Spurgeon at the UC Berkeley Botanical Garden years back at a Michel Garcia workshop. We immediately connected on mushroom dyes and have been sharing tips and tricks on our experiments and results working with mushrooms for color. Michael has been incredibly generous with his knowledge and gifting mushrooms to me to include in the Mushroom Color Atlas, including Cortinarius californicus and passing along Neoboletus praestigator from Norway.