I have never encountered this term, but it sounds like a portable form of raw materials. I am using Dictionary of Glass by Chas. Bray. According to it, glass makers use batch and cullet to create the molten glass for their work. Batch is generally understood in this book as the individual raw materials like sand, while cullet is recycled glass. There now being a shortage of the latter, pelletised batch is now sold. These are glass balls created from batch. Since this concept of batch is new, I would go with cullet, which can be modified in this instance by bar-shaped.

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Note added at 6 hrs (2010-06-22 08:28:47 GMT)
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I looked at 'melted cullet', but melted seems to be synonymous with molten, i.e. in a liquid state. But another site does have 'The melted cullet is molded into the desired shape' and there is no reason why it cannot be an intermediate shape suitable for transport and storage. Presumably they made a large quanty of glass from batch at one time, perhaps elsewhere, and then used most of it for cullet so that the craftsman could remelt only what he needed at that time. Oddly, cullet has different properties than batch, so calling previously made glass batch would be a mistake, leaving only cullet. I checked 'cullet bar' and cullet ingot' but without luck. I checked 'cullet pellet' (2 hits) and 'pelletized cullet' (1 hit). So cullet bar on that principle would be possible, but 'cullet bottle' yields 92 hits, 'bottle cullet' 3620 hits, but that refers to the source more than the shape. 'bar cullet' yielded only one suitable hit. There were no hits for bar-shaped cullet' although it would probably be more undrstandable.