Which of the following was a preliminary step in making a stained glass piece
a.

artists cut individual pieces of glass

b.

the painters add details with emulsion

c.

designer drew a composition on a wood panel

The answer is "c.  designer drew a composition on a wood panel".

The term stained glass can allude to colored glass as a material or to works made from it. All through its thousand-year history, the term has been connected only to the windows of holy places and other noteworthy religious structures.  

As a material stained glass will be glass that has been shaded by including metallic salts amid its fabricate. The colored glass is made into recolored glass windows in which little bits of glass are orchestrated to shape examples or pictures, held together (generally) by portions of lead and bolstered by an unbending edge.