Is this a ring that you cast or was it a purchase that you made and it was cast by someone else?
I have used boric acid and alcohol as a flux and fire coat for years. And it has reduced my experience with scale significantly. I think that from what I see in the photo you will need to sand that off. It looks pretty deep. As a last resort on jobs I couldn’t do over for one reason or another I have had some success with using a 50% distilled water and nitric acid dip to remove scale but it isn’t a sure thing and you run the risk of other damage to your work. The obvious precautions apply ventilation, eye protection, baking soda at hand, etc if you try the dip. I feel like I repeat this often but look into Tim McCreight’s book complete metal smith books. I would try again to abraid the scale off the work first and use the dip as a very last resort.