I wanted to achieve the effect of bubbles or rainbow clouds in an illustration last week so I returned to a technique that I used to teach, which is using nail varnish to marble or print the paper.
You will need:
An old plastic container
nail varnish (various colours)
paper cut to size.
Fill your plastic container two thirds full of water the size of this container dictates the size of work you will make.
Then have as many nail varnish colours as you can. I would advocate trying to get your friends to donate their old or unwanted nail varnishes. carefully pour onto the water surface nail varnish. I like it when it spreads like the blue and yellow in the picture above, you can blow the surface to try to spread it, but it depends on the consistency of the varnish.