How to "seal" paint on glass?

If I am painting on glass with acrylic paints, how do I seal the painting so that it doesn't scratch right off? Right now if I rubbed the paint with a cloth or scraped my fingernail across it, it will scratch right off. Any suggestions?

Thanks!
Update: For Fantasies by Mel: I have never done anything like what I am doing right now. I am not a professional. I am flat-*** broke and trying to make a Christmas gift for someone special to me. I am using what I had on hand and was not aware when I began that it would scratch off so easily which is why I came to... show more For Fantasies by Mel:

I have never done anything like what I am doing right now. I am not a professional. I am flat-*** broke and trying to make a Christmas gift for someone special to me. I am using what I had on hand and was not aware when I began that it would scratch off so easily which is why I came to yahoo answers for advice... not criticism. I see from your webpage that you consider yourself a professional. It's a shame your attitude doesn't convey that also.
2 answers 2