One of the easiest and most amusing methods for decorating glass is one you rarely hear about, the shard. Shards come in endless shapes and many sizes so no two are ever alike and they can be applied in a purely spontaneous manner which can yield fascinating and unexpected results. I have used them over clear tubing, or on colorcased rod and tubing with equally rewarding results. The possibilities are endless.
There are several different ways to make shards, but the easiest and most fun is the coil bubble. I use 10mm quartz tubing as a blowpipe and simply coil colored borosilicate glass around the tip until the coil is about five-eighths to three-quarters of an inch long and sealed at the end. Heat the coil until it contracts and smooths out the ridges. Care must be taken to keep the wall thickness consistent, so you may have to blow the bubble out a little and shrink it back again once, or twice, to be sure. Then, blow the bubble out to a diameter of 1" to 2", depending on how thick you want the shards to be. Sometimes you may notice a strange vibration, almost like a hum, as the glass sets up. Allow to cool. Once the bubble is cool, a gentle tap will break it off the quartz blowpipe. Use a tweezers to break off any residual from the quartz tube where it was sealed to the bubble. If any tiny pieces of quartz get into a finished piece, it will cause cracking. Then, break the bubble into pieces. I generally like to leave the resulting shards as large as possible until I use them, since I can always break them down further, if I want to. Keep the shards labeled and organized. Empty film canisters will work, but a workshop "organizer" with plastic trays is ideal.
One of the neatest tricks I have learned is to make layered shards by coiling another color over the first. When a layered shard is applied, whatever color ends up on the bottom will rise up around the edge of the shard. For instance, if I make a shard that is root beer (NS37) over ruby (NS07) and apply it with the ruby side down, the resulting decoration will be root beer with a narrow rim of ruby! This will also work with multiple layering. If I make a shard that is ruby (NS06) over cobalt (NS01) over amber (NS13) and apply it with the amber side down, the resulting decoration will be ruby with a double rim of cobalt and amber! Note that the same shard will make a decoration that is amber with a double rim of cobalt and ruby if you apply it with the ruby side down! A word of caution, however. Layered coil bubbles are difficult to control and definitely take practice, so work up to them slowly.
Applying the shards is easy and fun. Enough heat must already exist in the piece so that just a touch from the flame will bring it up enough to accept the shard. Grasp the shard with tweezers and pass it through the flame quickly three, or four, times to warm it up. Then quickly heat the piece and the shard and just touch the shard to the piece to get it to stick. Heat the shard just until it softens, but not so much that you ruin its shape, and paddle it into the surface. Keep the [addle close to the shard while you are heating it. Sometimes the shard will want to flip up and over suddenly and having the paddle close to it will help prevent that from happening. Don't worry about paddling it completely flush with the surface. It is easier to heat and marver the entire piece once the decorating is complete.
Often, you will trap air beneath the shard. As you heat the shard for paddling, the air will contract into a bubble. Small bubbles are not noticeable enough to be a problem, but larger bubbles must be removed. Here's how. Repeatedly hit the bubbles hard with a highly oxidizing flame and allow them to cool for a few seconds. Each time the bubble is heated, the glass over the top of the bubble will become thinner. This is because the surface tension of glass tends to draw itself to where it is thicker. About the fifth or sixth time you heat the bubble, the expanding air will break it, leaving only a small dimple which can be easily heated out.
Finally, try not to be too methodical, or deliberate, about how you decorate with shards. Best results are achieved if the decorations are done loosely and quickly. Experiment with different color combinations. Add frit, trailing and squiggles. Go wild! So much of lampworking is so tightly controlled and precise, that it's great fun to work in such a carefree and spontaneous manner.