Repeated dry transparent layers deepened the tone but the colour lost brightness. What is the likely cause?

Correct answer: Too many layers reduced colour luminosity and made the mixture heavy

The governing glazing principle is that transparent layers modify the light returning from the surface. A limited number of dry glazes can deepen a colour while preserving luminosity, but too many layers increase pigment and optical filtering. Less light is reflected back brightly, so the result becomes heavy, dull, or muddy even though the value is deeper. Option C is correct; a clean brush, brighter paper, or insufficient drying does not explain this stated effect.