A Brittle Selvedge
I am having trouble with a selvedge thread breaking. I am using 8/2 tencel in the warp. I miscounted the warp threads so had to add one on one edge, and it is the selvedge thread I added that is breaking. The edge thread on the other side is not breaking. The weight I am using weighs a little less than 1 oz. Do you have any ideas on why this is happening?
If you feel the warp with your hand and the tension on the weighted thread feels the same as on the others, then the weight is not a problem. If the weighted thread feels looser, then it is free to pull in more, and that might be why it's breaking. If the weighted thread is tighter, it might be abrading against the reed more than the thread on the other side and therefore breaking.
The biggest issue is draw-in, though. If you have little or none, edge threads shouldn't break.
In case these edge threads are floating selvedges: a floating selvedge that you add and weight should be no more likely to break than one that is beamed and weighted. If you aren't weighting the one that is beamed, then my guess is your added one is tighter and you have some draw-in on both sides. The tighter thread is abrading more, and the looser one is accommodating the draw-in. You should really weight both floating selvedges and minimize the amount of draw-in for the smoothest edges.