Explanation:

A:
Plastic under filling
Some knobs are actually assembled with injected molded plastic (like a toy model!) as the under layer for a thin fragment of stone. Plastic is very susceptible to breaking, melting and falling apart. It may also contain obvious flaws such as bubbling and mold marks.
Poor Assembly
Upon close inspection, you will see this specimen is poorly assembled. Note the unevenness of the stones along the edges. Note also the chipped stone in the corner and the uneven stem shape.
Custom Cabinet Knobs & Pulls Guarantees our products are authentic gemstone knobs of the finest lapidary standards.

B:
Complete Stem
Actual Custom Cabinet Knobs are carved from a solid piece of genuine gemstone, like our quality Rhodonite (shown here). These also include the high quality brass insert and 4 different screw lengths for a perfect fitting pull stem. This ensures the distinctive durability and installation ease associated with our custom knobs.

C:
Glued Stems
Poor quality knobs, like the one shown in picture C, have the stems sloppily glued onto the back of a thin piece. Notice the flimsy appearance. They are easily broken away from the stem and thin pieces of stone are easily broken on impact.