How does black CuO impart a green color to glazes and glass?
This is due to the oxidation of cupric oxide.

The main componds believed to cause this colour comprise a mixture of 3 compounds: $\ce{Cu4SO4(OH)6}$ (green); $\ce{Cu2CO3(OH)2}$ (green); and
$\ce{Cu3(CO3)2(OH)2}$(blue).

The following reactions are believed to take place:

Copper (I) oxidised to the black copper (II) sulfide ($\ce{CuS}$)  in the presence of sulfur impurities. Under accelerated conditions, the described process occur at a faster rate.

$\ce{CuO}$ and $\ce{CuS}$  reacts with carbon dioxide ($\ce{CO2}$) and hydroxide ions ($\ce{OH-}$) in water (in presence of air) to form $\ce{Cu2CO3(OH)2}$.

The extent of humidity and the level of sulfur have a significant impact on how fast the compounds develop, (under controlled conditions these reactants are varied to produce a favourable hue) as well as the relative
ratio of the three components.

$$\ce{2CuO + CO2 + H2O → Cu2CO3(OH)2~~~~~~~(1)}$$      

$$\ce{3CuO + 2CO2 + H2O → Cu3(CO3)2(OH)2~~~~~~~~(2)}$$        

$$\ce{4CuO + SO3 +3H2O → Cu4SO4(OH)6~~~~~~~~~(3)}$$            

References


http://www.wskc.org/documents/281621/282063/ENGAGE_E3S_Chemistry_Statue+of+Liberty.pdf/e4f24c7e-3666-425e-9c41-7dbdd0065eb4