No, I was just using the burn tool as an example because that's the tool that was open at the time. In the case of the erasor, it's the opacity slider. But really, it's the same slider for every tool, just changes names for the tools. It's a percentage of effect. In this case, the lower the percentage of opacity/effect, the less it erases. In this way, you can make your mist more or less solid. At 100% it erases everything. at 0% nothing. Everything in between is just a gradation of the effect.

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