We have translated "fusion" as either "fusion" or "casting," depending on context. However, on 108v (a continuation of "Spalt" on 108r), there is the following excerpt:
Cela<lb/> <corr>s</corr>e fait ou dans la <tl>forge des <pro>orfevres</pro></tl>, dans un <tl>countour de<lb/> <m>briques</m></tl>, ou dans un <tl>fourneau à vent</tl> à fœu de fusion, de sorte<lb/> que le <del><m>sable</m> demeure <tmp>assés long temps</tmp></del> <add><tl>creusel</tl> demeure un <ms><tmp>quart dheure</tmp></ms></add> rouge.
This is done either in the <tl><pro>goldsmith</pro>’s forge</tl>, <tl>surrounded with <m>bricks</m></tl>, or in a <tl><fr>fourneau à vent</fr></tl> with <fr>foeu de fusion</fr>, so that the <del>sand remains <tmp>long enough</tmp></del> <add><tl>crucible</tl> remains red for a <ms><tmp>quarter hour</tmp></ms></add>.
Can we translate "foeu de fusion" as either "casting fire" or "fusion fire"??
Well, I really don't know what that means, but I think "fusion fire" is ok...a really hot fire? NB it should be "goldsmiths' forge" not singular.