affinity photo · HeyBraza shows you
affinity photo mask brush not painting
HeyBraza spots why your brush does nothing on the mask - wrong thumbnail selected, white-on-white, or zero opacity - and points at the fix.
you select the paintbrush, drag it across a mask, and nothing happens. it's almost never a bug - it's one of a few setup mistakes. here's how to tell which one is yours and get the brush working again.
short answer
two causes: you're painting on the image thumbnail rather than the ringed mask thumbnail, or you're painting white onto a white mask. press 'x' to swap to black, and check brush opacity and flow aren't near zero.
or do it yourself
- 1check you've clicked the mask thumbnail (the ringed one), not the image - painting on the image won't show on the mask.
- 2look at your brush colour: on a white mask, white paint does nothing - switch to black to hide, or press 'x' to swap black and white.
- 3in the context toolbar, make sure brush opacity and flow aren't near 0% - set both to 100% to test.
- 4confirm the brush 'blend mode' is 'normal' and you're using the paintbrush, not the erase or selection brush.
- 5still nothing? the mask may be hidden - toggle its visibility, or zoom in to check you're painting inside the canvas.
steps last checked

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downloadcommon questions
i'm painting white on the mask and nothing shows - why?
the mask is probably already white, so white-on-white is invisible. paint black to hide pixels, or press 'x' to flip your colours.
how do i know i'm on the mask and not the layer?
the selected thumbnail has a highlight ring around it - click the mask thumbnail so the ring is on it before you brush.