I am amazed at the results. Much better than I thought. They were all rinsed with water and then put in the dishwasher to ensure all the caustic soda was gone. Probably a bit OTT but hey. The oven trays have come out clean but seem to have a coating of white powder on them. I initially thought it might be caustic soda but now thinking it is unlikely given the level of rinsing etc. Any ideas? Is it safe to just wash it off by hand? Was thinking of using vinegar to neutralise it if it was caustic soda.

Maybe I am worrying too much. After all the warnings about caustic soda wanted to be careful