one question on porcelain

Dear pottery lovers, I am trying to find an answer to a burning question I have regarding porcelain painting. I would really appreciate if anyone might be able to lead me to the answer. I am a ceramics sculptor who wants to move to sculpting in fine porcelain. I bought some porcelain clay and made a number of realistic, detailed bird sculptures, with lots of feathering and rough surfaces. I then read a book on porcelain painting, ordered some paints, applied the first layer of colors to two of the pieces (with glycerin and water) and fired at cone 018, which was the come reccomended by the paint manufacturer. The result was such a total disaster! The paints do not look fused and glossy at all like the beautiful ones I admire in the book I read or displayed in stores. The colors look muddy and not bright, not at all as shown on the color charts. My unpainted pieces were too rough to put the paints on nicely and no brush worked to smudge the colors. I am wondering if I should have coated the pieces with a clear glaze of some sort before having painted on them. If this is what I should have done, could you please tell me what this clear undercoat of glaze might be and recommend a brand? Are there any other things that might have gone wrong, like could it be that I have used the wrong cone? Thanks again for any help, Asli Cetinel