Greg;

The 'goop' has to be between 90 and 110 deg F, and can be just about any viscosity you want from thick to thin, as long as you coat the required amount of silver per unit area.

It can be made to be as thick as the current inks, but would have to be hot as above.

The paper would have to absorb the liquid, or it would have to be somehow kept flat to dry.

PE