Attribute-driven shader parameters (transparency) turn material black

[zbugni]

Hello. I'm making a simulation of dripping candle wax, and I'd like the droplets to start out watery and transparent but become opaque and waxy as they solidify. For reference, see the puddle of wax pooling around the flame compared to the rest of the candle.

To do this, I am using a custom temperature attribute, which is bound to the transparency and roughness values on a principled shader, like this-

For the most part, this gives me the effect I want. However, in areas where the temperature approaches its maximum value (100), the material looks black and burnt.

Does anyone know what could be causing this? It's frustrating, because I very nearly have the effect that I want. Any help would be greatly appreciated!

Here's my project file: CandleWax7.hipnc

[TobyGaines]

Every time I see black in transparency, the first thing I think is that ray settings are too low / not a bright enough environment to refract / exit color needs some value in it