The reagent that gives a brilliant red precipitate with nickel ions in basic medium is dimethylglyoxime (DMG) or its sodium salt, sodium dimethylglyoximate. This reaction is commonly used in qualitative analysis to detect the presence of nickel ions in a solution. When DMG is added to a basic solution containing nickel ions, a red precipitate of nickel dimethylglyoximate is formed. This reaction is often used as a confirmatory test for the presence of nickel ions.

${\mathrm{Ni}}^{2+}+2{\mathrm{dmg}}^{-}\to \left[\mathrm{Ni}(\mathrm{dmg}{)}_2\right]$