[wickedglass]

I've had this with a caramel type colour before, back in the early days and also seen it in NS Exotic Red. It is pooled metal which turns into wires when pulled into a rod. If you do a caramel overlay, blow it up and sandblast the surface of the vessel away, you can see small areas where the silver has pooled under the skin. I've never seen it that bad before, that's pretty full on. It is possible that your rod was pulled out from near the bottom of the furnace where the metal has sunken to and gathered in a higher density. Obviously the glass is somewhat different coming from different areas of the furnace ... it has to do with the way the heat distributes throughout the tank ... from the corners, the sides, the bottom and top. Depending on how efficient the furnace is in heating evenly and thoroughly, it's even possible to get differing COE from the same batch due to this.

I must say that I've never heard of "chunk copper" being used when batching and it doesn't make much sense to me; it seems like a haphazard way to go about making glass ... especially considering that glassmaking is a scientific process, already fraught with a large amount of possible variables, and the aim is to make a batch as repeatable as possible. The glasschemists I know use ground and powdered ingredients which they can distribute evenly throughout the batch.