For years I've wondered the best way to clean older crochet thread, doilies or any thread crochet of the age spots & other types of aging of thread, without damaging it. BLEACH is an absolute NO-NO! Or liquid laundry soap with bleach or even with colorsafe bleach is also a  NO-NO! So how would you get the results you want? Add some HYDROGEN PEROXIDE to your delicates cleaner (Woolite, liquid glycerine, liquid laundry soap w/o additives)! It works! It brings back the original luster & sheen of your older thread. I crochet the item I want from the thread & then put cold water, about 1/4cp. hydrogen peroxide, and the soap in an ice cream tub with a tight fitting lid. Then shake it up real good & set it down for at least 6-12 hours. Then check your item by rinsing it under cold water. If it hasn't come out, repeat the process by putting it back into the same solution  & let it set another 6-12 hours. Repeat this process as many times as you want, because you won't damage the thread. Always check your thread for strength by pulling a piece between both hands. If it breaks easily then it's too old to use. If it takes quite a bit of pulling to break it, then it's still in usable condition. I hope that this helps someone out there. It sure helped me.  The only thing I use older thread for is for myself & family if they pick out older thread. But it's nice to know that it can be cleaned & the beauty of the thread can show itself once more.