Sodium orthovanadate synthesis
From Supniewski, J. "Inorganic Preparative Chemistry", 1958 (in Polish):


  Melt $\pu{36.4 g}$ of vanadium pentoxide $\ce{(V2O5)}$ and $\pu{63.6 g}$ of sodium carbonate $\ce{(Na2CO3)}$ a nickel crucible until you get a uniform, clear melt with no bubbles of $\ce{CO2}$ coming out. Pour the melt on a cold plate and wait until it solidifies to a colorless mass (during the cooling process it should turn dark green, then yellow, then colorless). Pulverize the melt and dissolve it in a minimum amount of cold water, filter, and layer with several volumes of ethyl alcohol. After several hours, colorless crystals of $\ce{Na3VO4 * 16 H2O}$ should separate. Wash the product with ethanol and dry in a desiccator.


Some clarifications as requested in the comments:

"Minimum amount" means that you need to add only so much water to dissolve the salt completely, no more. Just add water in small portions and stir well - if the salt is still visible add some more water, etc. Suppose it took you about $\pu{50 mL}$ of water to dissolve your substance. Now you need to add twice or thrice (i.e., $\pu{100 .. 150 mL}$) the amount of ethanol ("several volumes"). Add the alcohol slowly so the solutions do not mix immediately but form two separate layers, and leave it undisturbed for several hours (I think it may take a day or two).