Yes, I agree the comments of Prof.Isaac .

In my point of view, i see the flux floating on the melt during the reaction period actually protects our melt against any bad effects from environment.In such case, if a melt is stirred mechanically then it will bring few issues such as addition of inclusions , contaminants , oxide formation etc like said by Prof .Isaac.

There is an another way usually we do ,that is Controlled stirring can be done with in protective environment using inert gas purging.