The four C's of diamonds are an essential set of criteria used to evaluate the quality and value of a diamond.

1. Cut: The cut refers to the diamond's shape, proportions, and quality of its facets. A well-cut diamond reflects light beautifully, creating sparkle and brilliance. It directly affects the diamond's overall appearance and is crucial in determining how light interacts with the stone.

2. Color: The color grading of a diamond determines its level of tint, starting from completely colorless (D) to light yellow or brown shades. The most valuable diamonds are those with little to no color, as they allow maximum light to pass through and create more brilliance.

3. Clarity: Clarity assesses the presence of any internal or external flaws, known as inclusions and blemishes. Diamonds with higher clarity grades have fewer imperfections, making them rarer and more valuable. However, most diamonds have some form of imperfection which can only be seen under magnification.

4. Carat: Carat refers to the weight of a diamond and is often misconstrued as the size. However, it is important to note that carat weight does not solely determine a diamond's value or appearance. While larger diamonds can be impressive, smaller diamonds with exceptional cut, color, and clarity can have equal or greater beauty. Ultimately, it's the balance of the four C's that determines a diamond's overall quality and worth.