its bucket chem, dont worry about the reaction. You will wind up (stoichiometrically) with about 1/2 the weight of Boron trioxide by just driving off the water Basically you are creating an anhydrous boric oxide which is kinda glassy. Finally, youll wind up with about 1/10 reaction weight of boron from the oxides.
If you need high purity in your final product, be aware of your lab ware (I guess Id use high qual glass ware , maybe a wide mouth beaker over a burner)
The real problem is the driving reaction of the boric oxide anhydrite. You can add about 1/2 the weight of the oxide glass in Mg powder to make a boric oxide "thermite".
This will leave you a mix of boron "grit" MAg Oxide, and Mag boride. You want to drive those off with some .1 N HCl.
THERE IS A CAUTION THT ENTERS HERE. YOU WILL be creating a bunch of Boranes (Hex, tri and DIBORANE).
Diborane is pyrophoric as it is driven off (It will explode in air as a function of the product weight being produced) . At low amounts its "cute" , youll be making blue pops of diborane going off. If you start going commercial -youd better have collection means or youll do a massive rearranging of your lab hood .(Do this in a hood and wear all the arm and eye protection)
If you know your chem and can see the product balance from my"back formulation", you can do the stoichiometry and equivalent weight calcs .
Just be careful at the borane production phase.
When you react the HCL to collect the boron (itll be grayish black chunks) put in some Sodium Bicarbonate (like 1 or 2 g) to keep from etching your glassware.
Are you using this for pottery? or reacting double bonds or are you collecting something radioactive??