Whilst looking for a way to find out what size an antique crochet hook I have is (it says 4-20) I found the Antique Pattern Library, where individuals are uploading scans of antique patterns. I'm going to have fun browsing this!
If anyone knows what a 4-20 is, let me know. It looks about 1.5mm on my ruler.
Finished the basketweave blanket with two rows of double crochet. I think a wavey or ripple pattern is next.