Black

[Annie.]

Acrylic
I am trying to do a dark night sky.

I thought it would be richer if I use a blueish tone, like Payne Gray (just to find out that it was simply carbon black (PB 29) with ultramarine (PBk 7).

I am running into 2 problems with the Payne Gray:
1) It poorly covers the canvas, although the black part is labelled as opaque.  Already 2 coats and still not good.
2) I added 'open acrylic medium - matte', instead of the standard medium... to have more time to paint the background.  The paint now has a guey texture, which I dislike.  I mixed well, add few drop of water, no change.   Could it be a bad bottle of medium? (doesn't smell bad!)

I also have some Mars Black (PBk 11), but no Carbon Black.

Thanks

[nolan]

I never use medium, but I suspect that this is your culprit. There may be nothing wrong with the medium, but by adding it to your paint, it has made the paint less opaque.
As a result you have had to apply more paint. This thick layer of acrylic is now taking longer to cure that normal and may stay tacky for a while.

Put it in the sun, that will help it to cure sooner.
Tip - another way to create a blueish sky is to paint it black, let it dry, then glaze over a blue (like Ultramarine or Pthalo Blue)

[Annie.]

Thank you for the tips. 

Now that I think of it, I never see you adding medium to your acrylic.

I really like the idea of the blue glaze.

[nolan]

I don't even own a bottle of acrylic medium

[Annie.]

So you would only use a bit of water if needed....