That is most likely a stain or a very saturated cobalt. Most saturated cobalts are dark blue, I have never seen such a light blue like that with cobalt.
Look at these mason stains below.
https://www.theceramicshop.com/product/8693/delft-mason-stain-6320-1-lb/
https://www.theceramicshop.com/product/8703/copen-6368-mason-stain-1-lb/
https://www.theceramicshop.com/product/8682/vivid-blue-6306-1-4lb/
Note: Stain are usually between 3-10% in glazes. If you want to make (say a 5000g batch) you are better off getting 1 lb of stain, many people (myself included) often get 1/4 lb and it's a few grams off, and there is not enough for a batch.
Brandon Franks got a reaction from ImogenB in bright blue food safe glaze
Brandon Franks got a reaction from liambesaw in Free Video Recommendations for Potters
