There are patterns designed specifically for tiles, but you don't have to limit yourself to just using tile patterns. If you find a stained glass pattern, you can easily adapt it for mosaics.
The main difference between a mosaic pattern and a stained glass pattern has to do with the spacing between the COE glass pieces and the size of the individual pieces.
Many mosaic pieces are used outdoors. Due to the range of temperatures that exist outside, mosaics made from large pieces of glass will crack over time. To avoid this, make sure the glass is well seated in the cement and that there are no air bubbles under the glass. Another way to avoid cracking is to use smaller pieces of glass. The larger the piece of glass, the more likely there will be cracks in the future.
Another factor to consider is the amount of space between the individual glass pieces. Depending on the pattern you use, the spacing between the glass pieces should not exceed 1/4 inch.
To convert a stained glass pattern to a mosaic pattern, you must first resize it to fit the size of your mosaic mold. Next, cut the individual pieces of the pattern 1/16 to 1/8 smaller. If you want the look of traditional stained glass, cut the smaller 1/16 individual pieces. The spacing of adjacent glass pieces should be uniform.
If the pattern you have chosen has large pieces of glass, cut out these pattern pieces (1/16 inch smaller), then divide that pattern piece into smaller pieces with 1/32 inch space between the pieces. Using this smaller space within the design, where a large piece of glass used to be, will convey unity and prevent future cracks.
If you are not using a clear mold, place the clear contact paper sticky side up on top of the pattern. Proceed as if you were using a clear mold until all the glass is on the contact paper (upside down). Then carefully place the glass contact paper in your mold.