After a quick trip to the hardward store, where I found multiple sizes of washers, I picked up the necklace clasps and rat tail satin cord at my local craft store. I already owned the metal letter stamps and a hammer.
Then, I set to work on the concrete. Eleven washers later, I was happy with how it turned out. (Never attempt making these necklaces with a curious toddler at your side!)
There are about 10 more necklaces that I want to make, but I'm not sure the city of Seattle has enough washers for all of my mistakes! But, I think they're just too cute not to try, try again.