Left: "Under the Sea" cake from Kok, P. S., Yow, A., Khandadi, A., & Hongde, L. (2014). Step-by-step Cake Decorating with Cherylshuen. Singapore: Marshall Cavendish International [Asia] Pte Ltd.
When considering what counts as a "professional" or "authoritative" source for your art form, consider-- is the information created by someone who is professionally employed in your art form's field (or a closely related field), or are they a hobbyist?
If you are looking at an older or more generic source of information, such as a manual or cookbook, consider-- who was it created for? And is it considered a "classic" or "major" work in your art form's area-- you might have to do some additional searching to figure out what people are saying, if anything, about the work!
