Have you seen pieces that have a bunch of lines that seem to have been drawn right next to each other? This is done in a couple of different ways but as of lately most are done using linework tubing. This tubing is made using 2 tubes of clear glass with rods of color in between them. Then the artists melts all this together into one tube. After that tube is completely melted together, they can then pull off sections of it to make the different pieces.