applying black mask makes layer completely transparant

[RealPixels]

Hi, I'm trying some skin retouching and found some tutorials for that. Following the tutorials I do:
duplicate layer
frequency separation
select low frequency layer
apply gaussian blur
apply black mask on that layer by alt clicking the mask layer icon.

Doing the final step results in my low frequency layer becoming totally transparant, hence unusable.

What is happening? Am I doing something wrong? It's doing my head in
 

I am on affinty 1.10.5.... on a win 10 pc core i5-6400, 16Gb ram and a lot of terra diskspace.

[GarryP]

Welcome to the forums @RealPixels

Using a black pixel in a mask tells the software not to show that pixel in the layer which is being masked.
Making the mask completely black tells the software to show no pixels from the layer being masked.
With masks: Black = occlude what is behind; White = let all the light through; Grey = something in between.

Think about a cartoon robber wearing a black mask over their eyes; you can’t see the parts of their face which are occluded by the black mask but you can see their eyes through the gaps.

In your case, don’t use Alt when creating the mask and it will start out all white.

[RealPixels]

tnx @GarryP for the response.

 

[thomaso]

4 hours ago, GarryP said:

their face which are occluded by the black mask

Is white the new black … or especially "chilling white" … 😉

[NotMyFault]

6 hours ago, RealPixels said:

select low frequency layer
apply gaussian blur
apply black mask on that layer by alt clicking the mask layer icon.

Doing the final step results in my low frequency layer becoming totally transparant, hence unusable.

What is happening? Am I doing something wrong? It's doing my head in

I assume the recipe might be a bit different 

1. add a gaussian blur filter layer instead of directly applying a blur, 
2. Nest the black mask to the filter layer,

In all cases:

1. paint in white on the mask layer where you need the blur effect.