"metail" occurs twice in the manuscript and has been translated once as metal and once as metal. It is not given as an alternate spelling for metal in the glossary.
See 16v: ...Tu pourras couler dans des moules & coquilles de fer ou de metail ...you will be able to pour into molds & iron or metal The editorial comment is "Here <i>metal</i> means not metal in general, but an alloy of copper and tin." 
87r: ...& jamays en ceste sorte le metail nentrera bien ...& in this way, metal will never enter the mold
QUESTIONS: - is "metail" an alternate spelling of metal and thus be added to the glossary? - is it ok that it has been translated with two different meanings of "metal"? Or, @ps2270, do you think that 87r should also be metal?