As CR-39 lenses age they deteriorate. A few years ago I came across some + spheres that had been peacefully sleeping in a box in my garage since I retired in 2002. Took a +2.00 out of its envelope and as expected it was schict brindle yellow/brown. I was also able to break it in half with hardly any effort. The lens was sort of “crumbly” From an impact resistand standpoint, totally unusable.

If its “yellow” toss it out.

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