Adding Weight to Glow Balls

Hello there guys! (^_^)
Ok, I've got me a couple of glow balls. Planning to make a Pendulum Poi set but with glow heads instead of the standard Stage Ball heads. The problem is that the glow balls are a little too light for my liking.

Can you guys think of any ingenious ways to add a little extra weight to the glow ball? Was contemplating sliding a nut or a couple of washers down the cord but realised that if I did, for a example, a horizontal throw with a flick, the nut/washer would slide up the cord to the handle end and throw the balance right off... thus ruining the illusion!

Thanks in advance!

-Dae-

Depending on how much you can get into them, a lead sinker may do the trick.

In theory you could also tie it on just above the ball I guess.

Yeah I'm going to need to cut open the ball anyway... so maybe slipping in some lead weights would do the trick! Just worried about how visible it would be... Though experimentation will be conducted!!

Rather than filling it with loose weights that will shake around could you fill it with silicon or similar that will set as a solid

I put sinker weights on my quick links. At first I just put one, but I noticed that it slightly altered my planes, but I got used to it and it stopped. One on each side was perfect. Cheap easy fix. But be warned, it can mess up your quick links.. I think so anyway (one of mine got messed up and I couldn't figure out how else it would've happened)

They also suck when you get hit with them. My knuckles have taken a lot of damage.

chunk of blue tac?

I would crack the ball open and spread a clear drying caulk around the inside of the ball so the added weight is spread evenly and light will not be interrupted