Years ago, I found a nice stash of ‘darning cotton’ at a thrift store, now it is depleted. This works great to blend in repairs since it was not mercerized. Mercerized thread gives it the definitive shine (about every brand of thread I find). I cannot seem to locate any thread today that has not been run through mercerizing process.  Ideas on where to find better options than shiny/mercerized thread for darning?  Thank you.