There are two methods I know of for making mandrel wound hollow beads. The first, which I use, is to make a disk that curves in slightly. It will usually slump into a more hemispherical shape as you make the second. Make certain the bead release is well heated and the glass nicely goopy for that first turn so that it adheres well to the bead release. Because hollow beads have so relatively little point of contact with the mandrel the concern is adhesion, not beads that won't come off. I heat the release to glowing—only for a second, but red hot none the less. I want that glass to stick.
Then, start a second disk, again taking a moment to preheat the bead release to glowing orange. The distance between the disks will be length of the bead. Wind the glass smoothly and evenly onto the disk, heating the rod, not the disk. The bead (to be) should be beside or above the flame at this point, not in it. If the disk starts wobbling and pulling out of shape the rod glass is too stiff and/or the disk glass is too soft (warm).
Don't worry if the disks are not the same shape. It's best to have them the same circumference, so they touch, but quite often one will be slightly larger than another. That's okay. When the disks almost touch, position them high in the flame to warm them, especially if you've been hearing ominous little crackly sounds. Wait for the cracking noises to go away (a few seconds) and position the edges of the disks in the flame. If one is larger than the other, that's the one you want to heat up. Otherwise heat both evenly.
Spin the lips of the disks rapidly as they heat to red hot; tangential—not centrifugal—force will cause them to flare out. Now use your marver to gently guide the lips together. Use one with fine textured graphite, because rough graphite will cause scum or small bubbles to form around the equator of your bead in some colors. I like Arrow Springs’ ‘Stump Shaper’. You can also use the edge of this tool to shove the lips together if mere stroking doesn't do the trick. If your bead isn't puffing, there's a leak. If you know you've done a good job making and guiding the halves together, try heating the ends where the glass attaches to the mandrel. Quite often it cools down enough to shrink and pull away, which is why you want it good and goopy for that first course.
Sometimes the earliest made coils get too cool and separate just enough to leak. If a coil is really standing proud and is much hotter (orange in comparison to everything else) gently tap or stroke it down with the marver to cool it. This will also help to seal leaks by keeping a more even temperature gradient across the bead. A good learning color is a dark transparent color, such as cobalt. It's opaque when hot, so the holes are easy to see; and transparent when cool so you can check your walls for thinness and eveness.
Of course, if you are just learning to make hollow beads, you may have voids and holes all over the place. (I certainly did) In that case, use a tool (my favorite is No. 5 forceps, also known as knotting tweezers) to close the hole. Big holes can be patched with a swipe of the rod. If all else fails, flatten the bead with mashers and make a heart out of it.
How to make a heart:
Make a disk by squashing a (failed) bead.
Heat one edge and make a cut perpendicular to the mandrel with a knife. Rocking the knife back and forth several times rather than attempting the cut all at once will usually give more evenly shaped and sized humps. This is the top of your heart. Heat the other edge of the disk, even letting it sag a little. Warm a rod or stringer touch it to the middle and pull. Blow, snap the rod off, and flame polish the break. Then flame polish the whole just enough to remove the chill marks and puff the heart a little.
Technique two for making a hollow bead is good for patterned cane beads. This was shown to me by Sally Prasch. Make a disk. Make a second disk (sometimes called a seed bead). Wind the rod from one disk to the other, twisting if you like. The first part, fanning out in a cup or funnel shape is easy; the challange is to start pulling back in, making the coils smaller. Contrasting disks give this approach a nicely finished appearance.
Hollow beads with cores in them: The core glass pulls heat away from the outer bead, so I think this harder than making a plain hollow bead. Make a cylinder. You can marver the ends into a gentle bicone shape, which gives a nice, finished appearance. Its length will be the length of the bead. Heat one end, preferably to orange-hot and start winding glass around to make your disk. When the disk is big enough warm the whole disk a bit; then heat the other end of the cylinder and start your second disk. It is very important there be a good join between the ends of the cylinder and the disk. Proceed as for regular hollow beads. You'll probably have to spend more time twirling the thing around to make certain everything stays warm, as the cylinder, and the mandrel it covers, tends to suck heat from the glass. You can of course decorate the cylinder before adding the disks. These should always go immediately into the annealer.
When you get good at those, give double, or even triple hollow beads within beads a try. I think it's easier to make them on 1/16” mandrels but they look so nice on a snake chain it's worth the extra effort to use 3/32”. Note that hollow beads typically must be spun more quickly than solid beads to keep the flame from boiling the glass, popping a hole in the bead (though this can have interesting design possibilities), or drooping off the mandrel. They are more apt to deform when rolled in surface treatments (e.g. gold leaf, frits and powders) but overcoming these limitations will give an excellent sensitivity to the heat base.
Cleaning hollow beads. I use a foredom with diamond burs cadged from my dentist to clean the holes. Then I use a waterpik to blow out the bead release. Then I place the beads, hole vertical, to drain the water out. Once you remove the beads from mandrel, proceed through these steps immediately, or the release can dry on the inside of your beads, even if they're under water, and even boiling them in soapy water may not remove it later on.
Cleaning double hollow beads is a pain. I soak them in water for awhile to thoroughly wet the release; then shove the beads back and forth on the mandrel to loosen and break up the release as much as possible. Another advantage of using 3/32” mandrels is that abrasive coated round sawblades will fit through them. Several jeweler's wax sawblades can be bundled together for the same task. Clean the holes of both beads as thoroughly as possible. Then string the beads on the thinnest wire you can find. (I use a bent up cleaning wire from my lynx, which is 0.0138”, roughly 27 gauge, or 0.35MM thick) and waterpik it thoroughly. With the wire still in place, wrap an absorbant towel around the bead and shake vigorously to remove as much of the water as possible. Repeat with the waterpik if it doesn't look perfectly clean. Then, string it on a slightly stiffer wire and upend it. With luck the water will drain out along the wire, leaving no residue behind.
Unless otherwise noted, text, image and objects depicted therein copyright 1996--present sylvus tarn.Sylvus Tarn