Casing color inclusions, that is, trapping colored decorations inside clear glass shapes, is a technique that should be an important part of every hot glass worker's repertoire. Few kinds of decorations are as compelling or interesting to look at as one viewed through a thick mantle of crystal clear glass. Glass blowers working at a furnace with puntis and blowpipes are able to achieve stunning effects simply by repeatedly dipping the piece in molten clear glass and shaping the resulting gather. For lampworkers however, the problem is a bit more dicey.
That is not to say that lampworkers cannot do inclusions. Quite the contrary, lampworkers are able to do a kind of decorative inclusion that would be, at best, impractical for our off-hand brethren. This method is actually a form of hot "lamination" done by hand at the flame. When done correctly, it can yield very beautiful and complex colored forms entirely encased in clear glass. If done incorrectly, it can lead to disaster!
The procedure is begun by forming a cylindrical plug. It is important to select the proper diameter of glass and then to maintain that diameter while forming the plug. I generally use 1/2" rod to make small pieces and have used 1.25" rod for very large ones. The best sizes to use to learn the procedure would be 5/8" or 3/4" rod. Since this method consists of joining together two halves (with the color inclusion in between), the two halves must be the same size and shape. Therefore, it is very important to keep the initial diameter when forming the plug. Keep your ends evenly rounded and marver them using the diameter of the unheated rod as a guide. When the end is nicely formed, attach a handle, usually an 8mm x 10" rod, to the end. Switch hands and measure up the rod a pre-determined distance, say 2", and burn the big rod apart there. Finish the second end the same way you did the first. You should then have a plug that looks for all the world like a Vienna sausage attached to a 10" handle.(see diagram 1)
Next, the plug must be flattened on one side only. While it would be easier to simply heat the whole thing and flatten it evenly, when the lamination is done, the resulting shape would be closer to square than the desired cylinder. So, to save work in the long run, take the time now to carefully flatten only one side of the plug. This is done by first letting the plug cool until the color is gone, then, holding it vertically so it is less likely to sag, pass the flame up and down along the side of the plug. Do not rotate the plug. You want to only heat one side. To evenly heat the one side, periodically flip the plug vertically to the other side of the flame and heat the side from the other direction. In a few moments, one side of the plug should be glowing hot. Set the plug hot side down on a graphite plate and, using a graphite paddle to push with, press the plug until it is about 1/2 its original thickness. The resulting cross section should be flat on the bottom and domed on the top. (see diagram 2)
Now, it is time to add the color. It is applied to the flat side of the plug in any form you desire, striping, trailing, frit, shards, squiggles, whatever you feel like. For this example, we will use simple striping and some frit. When applying the striping, remember that the decoration will eventually be twisted so, if you want the twisted decoration to be straight, you must get the stripe in the center of the plug. This is more difficult than it looks. Multiple colored stripes can be applied at this time, but they still must be centered as closely as possible. To apply the stripes, simply heat and wipe the tip of a colored glass rod down the center of the flattened side of the plug. Good colors for striping are Northstar Ruby, Orange, Amber, Cobalt (the darker the better), Tourquesa, Multi and transparent Green. When the striping is complete, re-heat the flat side and re-flatten it as you did before. (see diagram 3)
Now, add some frit. Frit is made by crushing up colored glass. When glass is crushed, a wide range of sizes usually results. If you don't want to go through the trouble of screening the frit to get the size you want, you can simply shake the frit out of the crusher or container onto a sheet of paper. The larger chunks will roll out first. Simply wait until you see frit about the size you want and then sprinkle it onto your marver board into a little pile. Good colors for frit are Northstar Ruby, Orange, Root Beer, Turbo Cobalt, Black Hole, and any of the exotics. Arrange the pile into an oval shape about the size of your plug. Then, give your marver board a gentle shake to even out the distribution of the pieces of frit. Heat the flattened side of the plug again and place it carefully on the pile of frit. Press down with the graphite paddle to pick up as much frit as possible.[8] Re-heat the flat side to melt in the frit and then re-flatten as before. The first half of the piece is now complete. It should be smooth and even on the flat side with the color decoration completely melted in. (see diagram 3) Store it in your annealer with the handle sticking out of the worm-hole.
Make a second plug as close as possible to the same size and shape as the first. Compare with the first as you are making it to be sure. When it is complete, retrieve the first plug and heat them both together. A good way to do this is to position them so that the flame is directly between them striking them both simultaneously. On larger pieces, I sometimes bend the handles 25 degrees or so to enable me to get both flattened surfaces in full contact with the flame. Be sure you hold the two pieces directly opposite each other. This has the effect of neutralizing the tendency of glass to radiate off the heat it absorbs because it simply radiates the heat into the other piece. The heat is trapped and the pieces heat up much more quickly. When both flattened surfaces are glowing hot, quickly seal them both together. It does not matter how you do this so long as you do not trap any air. The two handles can end up on the same end or on opposite ends. It makes no difference which. It is, however, very important that no air is trapped when you bring the two halves together. To best accomplish this, start at one end and push the two halves together watching through the glass as the seal is formed. You will be able to see quite clearly if the seal is not properly formed or if any air is trapped. Sometimes it helps to set the piece down on a graphite plate while it is still hot enough to move and press it with a paddle. With a little practice (and a few failures), you should be able to perform the seal without trapping air.(see diagram 4)
Burn off one handle and pick off any nasty or bubbly bits left on the tip. Now, reheat the end of the joined plug until it is fairly soft and marver it. You want to get back to the "vienna sausage" shape you had at the beginning only now it will be twice as large. But be careful. There is a further danger of trapping air since there is a deep crease where the two halves are joined. Trapping air here is caused primarily by under- heating the glass before marvering. To keep this to a minimum, get the piece as hot as you can and then marver it gently watching for any places where the crease might fold over and trap air. Marver the end into an approximate semi-sphere and switch ends. Repeat the procedure for the other end and then marver the entire shape into a cylinder.(see diagram 5)
The last step is a fun one! Re-attach the second handle so you have a handle on both ends and reheat the entire joined plug. It is important that the plug be re-heated evenly so the decoration twists in a consistent manner. As the plug starts to soften, induce a twisting action to your rotation by slightly delaying the rotation in one hand. As the plug twists, it may lose its cylindrical shape. Before it gets too misshapen, take the time to marver it back to a cylinder as you go, then continue twisting. How much twist you give the plug is up to you, but I have found that not enough turns isn't very interesting, and too many ends up looking too busy. For most purposes, six to eight turns is usually sufficient. When you are done twisting, marver the plug back to a cylindrical shape.(see diagram 6)
That's it! Check out the decoration. Notice that the frit is only on one side of the twist. If you want it on both sides, you simply apply frit first, then stripe, then add more frit. It should be fairly obvious that there are endless possibilities here for decorations. Experimentation should be done liberally! It is also possible to do more complex laminations than the simple single one I have described here, but that is an area I am exploring right now. I'll let you know what I find!
Your plug with the included decoration can now be shaped into anything you wish. I have made them into many shapes and used them for many kinds of purposes. The accompanying diagram shows only four very basic ones, but in reality, any shape at all is possible. I am partial to cones and spheres but your tastes will probably differ.
I should mention here that a piece of glass with a colored inclusion will be more sensitive to thermal shock than a pure clear piece the same size and shape. There are small differences in the expansion co-efficient between colored glasses that, while it does not make the glass incompatible, does make it so they are less happy about being abused. Avoid placing a cold included piece in a hot oven. Forget sticking it in the flame! Whenever possible, try to use your included piece when you make it or as soon thereafter as possible. Make sure they are thoroughly annealed! Be especially careful when including Northstar Blackhole or any of the exotics. Avoid including Northstar Jade.
