Soap Gone Bad

I recently had a batch of failed soap; soap in which the oil separated. Today, I did my first rebatching of a soap, adding the failed batch to a small amount of milk with a little additional lye. I warmed it all in the crockpot until it melted, then repoured it into the mold. It's probably the ugliest soap I've ever made, but so far, it looks like it will harden up like it's supposed to. In looking at likely reasons for the failure, I'm guessing it was due to combining everything at the wrong temperature. In the 12 years I've been using the thermometer, it's never been calibrated. Joseph showed me how to do that, & lo and behold, it was 10 degrees off, which meant I let it cool 10 degrees too much before combining. Another possibility is that I made an error when weighing the lye, which is why I added a bit more. It's a good day when I've learned something new.