Reddit mentions of Amaco LG-10 Lead Free Liquid Gloss Glaze, Clear, Pint 16 Oz

You need to buy glazes, which depending on how much variation you want is probably going to cost you anywhere from 10-20 dollars a per color if you want the expensive stuff, however you can probably buy a set of 12 underglazes for about 47 dollars and a pint of clear glaze for about 10.

If you go this way, it's pretty similar to painting regularly, all you have to do is slap a few coats of clear glaze on it after you have the design on it and find a ceramics studio that will fire it, the place where I live charges about 2 dollars a pound for each peice or about 60 dollars to rent an entire kiln.

Here's some underglaze sets and a clear glaZe you could use, but you should check the nearest studio to see if they have any discount glazes
http://www.amazon.com/gp/aw/d/B0044SATSM/ref=mp_s_a_1_2?qid=1415905256&sr=8-2&pi=AC_SX200_QL40

http://www.amazon.com/gp/aw/d/B003IGIDR0/ref=mp_s_a_1_1?qid=1415905406&sr=8-1&pi=AC_SX200_QL40

http://www.amazon.com/gp/aw/d/B0044S97QW/ref=mp_s_a_1_6?qid=1415905420&sr=8-6&pi=AC_SX110_SY165_QL70