How Seed Beads Are Made
I found this online - somewhere - so I didn't write this and can't verify anything about it. I do have some comment son it though after it.

The earliest seed beads of European manufacture probably date to about 1490. Around that time,
Venetian glassmakers rediscovered the method of making beads by drawing molten glass into long hollow tubes. "Although a great deal of secrecy has always surrounded the drawn-glass beadmaking operations & descriptions written in 1834 and 1919 apparently represent procedures unchanged for centuries." A description of how the French seed beads are made today closely parallels these early accounts, indicating that even with the modern technology of the late 20th century, the beads you buy today are basically made the same way as those made hundreds of years ago. In the modern French method, high quality sand is "placed into a caldron and slowly melted to liquid form over a period of 21 days while the temperature slowly rises to its peak temperature of 1300 c - 1500 c." At this time, colorants and oxidants "like copper, cobalt, bauxite and even precious materials such as 24ct gold" are added to color the glass to the desired shade.

At this point, the molten glass is drawn into long, thin tubes. Historically, "a hollow globe of molten glass was attached to two metal plates with rods. Two men, each holding one of the rods, ran quickly in opposite directions, drawing out a tube of glass at least three hundred feet long. The original bubble of air remained as an orifice or tunnel running the entire length of the tube." The modern French method is similar but the stretching is performed by a machine instead of the mad-dash method.

The stretching phase is quite critical as atmospheric changes can affect the final bead color and the speed of pulling affects the final exterior size and the hole size. "The pulling of the molten glass creates the size difference itself by which the first sections pulled become the small sized beads since they are pulled farther, while the glass towards the end of the pulling process are larger in size since they are pulled not as far." These long tubes are then cut into small sections called "canes."

The canes are sorted for size and then cut into small tubes which will eventually become the final bead. The beads are finished by "reheating techniques (tumbling and constricting) or by lapidary methods (grinding)." In the modern French process, the unfinished beads are "mixed together with crushed charcoal, sand, and liquid plaster" and "placed in another furnace and heated while rotating to 800 c which shrinks the tube to its permanent form of the round bead." This is another critical step in the process because the heat creates the final roundness and the real color of the bead. Until this final step "the real color of the bead has not been seen. They have been colorless the precedent steps, which also creates the uncertainty if the correct shade has been achieved."

The beads are now complete and are ready to be cleaned and packaged for shipment. The entire process has taken as long as 60 days to create a single color. As you can see, there are many steps in the process and even a slight variation can have a major effect on the final size, color, and shape of the bead.

Hopefully, you now have some insight as to why every batch of beads we get can be a different shade and why it is almost impossible to obtain perfectly sized and shaped seed beads.
 

REFERENCES
The History of Beads by Lois Sherr Derbin, 1995
Bovis Bead Co Catalog, Pierre Bovis, 1998

 

Grizel's Notes on this:
Well, I will say I have proof on this site that seed beads did in fact exist WELL BEFORE 1490. And I know Germany made beads due to the medieval occupation name of the Bead Maker - Glasperlenmacher - seems to lead to the point that they made beads in Germany, and not seemingly endless belief that only Italy and Murano notably, made beads. Murano. I think they made the fancy beads, the trade bead as they were, the delicate and expensive, but the smaller beads were made in many other locations. Seed beads did not even seem to be as expensive in period as you would believe if they were to have been imported from Italy.

I personally, looking at square holed rochailles, cannot see how they could be produced in the 'run fer the hills' method. I know the trade style beads are made this way, but to me it seems more logical to run glass on wire (round or square) then roll it to make it even then cut it by rolling it across a bed of evenly spaced wires to cut and round them.

I imagine some sort of powder is used on these mandrel wires as beadmakers use on their bead mandrels now in modern bead making. I have seen such powder in my modern beads and from what I've heard the Czechoslovakians still make them the same way as they have for centuries, but never hear how that is exactly.

Some beads I have come across in my bags have points that look like pulled or wide blobs on one end as if it were on the end of a section of beads. That doesn't seem to fit with the above method. Having played a bit with glass beadmaking (just a bit) it feels like THICK taffy. If you poke it with a object it's like poking bread, the area around it becomes converse or bows outward which would explain the rounded angles and flat sides of the modern seeds.

I'm not sure I helped any, but I'm not sure the above is correct, but anyway that's my slant, not that you asked for it.

 
Copyright 2000 Jen Funk Segrest (Elspeth Grizel of Dunfort) http://www.medievalbeads.com