Bubbles and dirty baths

I am working on two different (maybe 3) projects right now.
One is an incredibly detailed realistic study of crab claws the other two are secret. I find I need to balance producing detailed work by doing more exuberant, experimental work and processes, and so I found myself bubble printing yesterday.
My bubbles are all black as I wanted the scummy effect of a not so clean bath. But of course you can print your bubbles in any colour and I am sure I will be making some coloured ones soon. Strangely for such a simple technique, I had to experiment in order to get the effect I wanted, and get quite technical.

Instructions 

Ingredients
A shallow tray (I used a roasting dish)
Washing up liquid
Paint (I used acrylic)
a hand whisk
a drinking straw
Paper cut to the size you require.

Technique
You make a shallow tray of coloured water diluting your paint.
Add a squirt of washing up liquid.
Stir it all up
Use your straw to exhale into the water and produce a carpet of bubbles over the surface.
If the print is not clear enough add more paint. If the bubbles not bubbly enough add more washing up liquid.

What I found is that blowing with the straw makes a nice even carpet of bubbles all the same size. But I did not want my bubbles all the same size, I found that if you whisk up your water you will make lots of small bubbles and then I used the straw to add larger ones. This produced a good variety and a range of marks. I also over printed many of them to fill in gaps or give them more impact if they were too light.