Painting black onto a layer mask

[LordyW]

Hi, I'm new to Photo but the following issue is driving me crazy - it may well be a beginner's mistake though..

 

I have created a Stack of photos that, together, form a background (opacity of each of these layers set at 12%).

I then open a file in a new tab of a portrait. I use the selection brush to cut out just the person from the background and then copy/paste it into the original tab, where it is inserted above all the background layers.

I want to mix some of the background image into the portrait, so I add a Mask Layer to the pasted portrait (a pixel layer).

However, when I use the paintbrush to paint black onto the mask, revealing the layers below [on the 'colour' tab both circles are set to black and opacity is 100%] it just paints black, as if I was not using a Mask. Also, on the little white box on the Mask line, it doesn't show a mini-preview of what I'm painting.

 

I've included a screenshot - hopefully it's a simple step that I've missed.. grateful for advice on how to resolve this

 

Thank you.

 

[MEB]

Hi LordyW,

Welcome to Affinity Forums

Make sure only the Mask layer is selected (clicking on its thumbnail in the Layers panel) and Uncheck Protect Alpha in the context toolbar (with the Paint Brush Tool selected).

[LordyW]

Thank you so much for the swift response, that solved it.