I check my balls with a "10x jewelers loupe" - not only old balls but also new balls. 10x really helps you see stuff you can't see with just your eyes. You can grab a "cheap" jewelers loupe for under $10 and it will last you a life time. They are great for checking fuse values and other hard to see items also.

Full disclosure I have been selling loupes for over 20 years so I always have lots of them around. Which just made me realize I should be listing some of them on eBay with my used pinball parts as helpful as they are when working with pinball machines.

OK guys now that I set you up go ahead and have some fun with the "checking my balls" statement above. I hear it all the time anyway - "pretty sad when you need a 10x loupe to find them" is the one I hear most often!