Making a marble ROUND
The #1 question I get asked as a marble maker is, "How do you make them round?" People just can't wrap their head around the idea of liquid glass being controlled in the first place, let alone how in the world a glob of hot glass ends up as a perfect sphere. This guide is about making a borosilicate (or hard glass) marble perfectly round.
The process for making each of these pieces round was exactly the same, and while not easy for the novice, it is overall fairly simple once understood. The main tool used is called a "marble mold" which is generally a piece of graphite with graduated sizes of half spheres drilled out of it. They come in many sets of sizes and it all depends on the size of the piece that you are working with that determines what mold you will need to use.
First off- to understand how an artist "holds" the piece, a "punty"- as it's commonly called- is used. This is a rod of glass, usually of a relatively small diameter and perhaps a foot in length that is attached to the piece. The artist uses this as a handle and turns it creating an axis that the glass is turned about to facilitate control and even heating (in a torch flame). Once sufficiently heated, the gather of glass is put into one of the "cups" of the mold that is larger in size then the gather all the while turning the punty and applying slight pressure to get a general round shape. The marble is then reheated in the flame with care not to melt the punty attachment. Once again, when sufficiently heated, the soon-to-be-marble is ever so gently set on the rim of one of the cups of the mold that is a smaller diameter then the gather. Again, during all of this the punty is being turned evenly and with added gentle pressure against the mold.
The key here is to change the angle of the punty relative to the plane of the marble mold's rim as the punty is turning. Slowly, the end of the punty (not attached to the marble) is raised and then lowered in a fluid motion all the while turning evenly. Lots of rotation, very little force is crucial. The gather of glass is forced by the rim, as it's turning, into the inherent spherical shape due to the round shape of the rim. Note, the heat base of the gather needs to be at the right point for this to work. The gather is hot and malleable on the inside but has a cooler skin on the outside.
The side of the gather opposite the punty is rounded at this point but only up to perhaps 2/3 of the marble is truly spherical. Another punty is then tenuously attached to the round side and the original punty is removed and the whole process is repeated. Only this time greater care is used due to the (purposely) weak connection of the second punty. With just about 2/3 of one side round, then just about 2/3 of the other side round, the two "round sides" overlap creating the true spherical shape of a marble.
Then the real skill in marble making comes into play. Removal of the final punty is THE skill that makes or breaks (no pun intended) the marble's roundness. The marble is set on either a Kevlar glove or a mobile marble mold and the punty is tapped from the side so it breaks off; the connection has to be done perfectly for this to work right. If any of the punty is left on the marble (a small chip) or if any of the punty was too attached and removes a small chip from the marble, the total volume of the marble has changed and therefore it will not be truly round when polished as the surface angle immediately near the punty attachment point will differ from the rest of the marble.
The difference between the talented/ skilled artist, and the master crafts-person is this final step. A marble is NOT round if this final step is only done to a "good enough" level. The marble is either truly spherical and perfect, or it's not- there is no grey area here. It takes an experienced collector to even see this difference but can be done simply by holding the marble so that a glare can be seen on the surface as the marble is rotated in the hand. If any distortion is seen in that glare, you know it's not perfectly round.
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