Master working is greyed out at the blacksmith. What am I missing?
your missing the proper forum to post in …
no game context
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go to the page for the game in reference of click on community and then forums and post there in general or help or support
The best place to ask is the Diablo 4 forum.
Masterworking is an end game activity that requires a high level item (fully tempered Ancestral item Ancestral Unique) and you need materials you get from the Pit activity. Tempering Ancestral items gives you two slots, not just one so be sure to put both tempers on it.
There are guide sites like Maxroll that have info on all the game systems like Masterworking as well.