I've been blowing bubbles with Jackson's Indian Ink on paper and encaustic:
I would never have tried this with previous indian inks as they are relatively expensive - the Jackson's Indian Ink is however very economical and comes in a large bottle making it easy to play with. Though its success did lead me to try some of my more expensive ones too...
The key to getting good bubbles is to use a decent detergent - the only one that I've found that does work available here in the UK is the original form of Fairy Liquid. You will also need to add water and ink. Experimenting with the quantities is part of the fun - start off with minimal water and add more if you think you need it.
Use a straw to blow the bubbles and make sure you only ever put the non-inky end in your mouth! I put a little piece of masking tape on mine with an arrow to show which way was up.
I tried several different ways of working with the bubbles - the best was putting them into a very shallow tray and blowing the bubbles big enough that they were over the edge of the container and I could "print" them onto paper without touching the edges of the dish.
Update 10 August 2016: Please note that the link to the ink will take you to Jackson's where you can buy this ink and in the process donate a few pence to me too!
If you have never shopped at Jackson's get a 10% first order discount using this link.
Enigma 666: Enigmatic 666 - From New Scientist #1821, 16th May 1992 [link] An “absolute difference triangle” is a triangle of numbers such that each number below the top row os equal ...