Hello! Thank you for your question. Here's the response from one of our glassblowers at The Corning Museum of Glass:
As you know a graal is typically done with a Swedish overlay or stuffing a cup.
If you choose not to use these methods but rather a typical color overlay, you will run into several problems. First, you will not be able to make the blank very large. Gathering over and blowing out a smaller blank will make your imagery and colors less sharp. Second, on the blank, the color will be as thick as the clear underneath - maybe thicker, which will make blasting or carving your imagery difficult and a thin blank is more problematic to gather over. If you work on a small scale, and won't be using complicated patterning or imagery, you may be fine trying this method.
Concerning your question about colors smearing together; it depends on your colors. Usually colors don't mix like that, but will remain in distinct layers. Again, this depends on color choice. Strong opals would be more likely to remain separate than using two transparents together. This will require some experimentation on your part.
I would recommend that you practice stuffing cups in clear as it is a very useful technique to know. I make my graals by doing a traditional color overlay and then blowing it into a thin cup which is then stuffed with the base color under two gathers of clear. You may also try sifting powder to do an "overlay" if you want to make a larger graal object. This works best with strong colors like enamel white or opal yellow etc.
To learn more about the graal technique and its history, see the questions linked below. Please do not hesitate to contact us with your glass-related questions in the future!
