I'm looking for waterproof black ink (India type) that won't dissolve when coated with "GOLDEN Matte Medium". I have tried several waterproof inks and they tend to dissolve. Any suggestions?
So much for the claims of "waterproof" inks"? It may be the amount of medium being applied, unless you see the inks bleeding immediately as the medium is applied.

Another approach is to spray a couple of thin coats of GOLDEN Airbrush Transparent Extender over the inks to seal them enough before applying the brush coats. If you do not have any airbrushes, you can use a really great device called a Preval® sprayer. This is a disposable aerosol can with a glass container you can fill with whatever you want to spray. It is used just like any other aerosol can. We recently bought one for $6.50.

You may wish to try GOLDEN Airbrush Carbon Black, perhaps made more resistant to the subsequent medium coat by adding the Airbrush Transparent Extender. We also have a Fluid Carbon Black that will require some thinning with water, but should develop a permanent film without lifting when mediums are applied over it. As a final note, it's important with paints to allow them to cure before applying the medium over them. If the films have not cured for at least several hours, there is a greater risk of lifting the color.