The 4 C's of diamonds are the criteria used to assess and determine the quality and value of a diamond. They are:

1. Carat Weight: Carat weight refers to the size and weight of a diamond. One carat is equal to 200 milligrams. Generally, the higher the carat weight, the more valuable the diamond.

2. Color: The color grade of a diamond refers to the presence of any color within the stone. The Gemological Institute of America (GIA) grades diamond color on a scale from D (colorless) to Z (light yellow or brown). Colorless diamonds (grades D-F) are considered the most valuable.

3. Clarity: Clarity refers to the presence of any internal or external flaws, known as inclusions and blemishes, respectively. The GIA grades diamond clarity on a scale from Flawless (no inclusions or blemishes visible under 10x magnification) to Included (inclusions visible to the naked eye). Diamonds with higher clarity grades are generally more valuable.

4. Cut: The cut of a diamond refers to how well it has been shaped and faceted. It affects the diamond's brilliance, sparkle, and overall appearance. The GIA grades diamond cut on a scale from Excellent to Poor. A well-cut diamond maximizes light reflection and is considered more valuable.

These four factors (carat weight, color, clarity, and cut) are used to evaluate and determine the quality and value of a diamond. It's important to consider all four C's when purchasing a diamond to ensure you find the right balance that suits your preferences and budget.

When it comes to selecting a diamond shape for an engagement ring, it ultimately depends on personal preference and style. Here are some popular diamond shapes to consider:

1. Round Brilliant: The most popular diamond shape, known for its exceptional sparkle and timeless appeal.

2. Princess Cut: A square-shaped diamond with pointed corners, offering a contemporary and elegant look.

3. Cushion Cut: A square or rectangular shape with rounded corners, known for its vintage charm and romantic appeal.

4. Emerald Cut: A rectangular shape with step-like facets, emphasizing clarity and showcasing a sleek, elegant look.

5. Oval Cut: An elongated shape with soft curves, offering a unique and flattering appearance.

6. Marquise Cut: An elongated shape with pointed ends, known for its elongating effect on the finger and dramatic appeal.

7. Pear Cut: A teardrop-shaped diamond, combining the brilliance of a round cut with the elegance of a marquise cut.

8. Asscher Cut: Similar to the emerald cut, but with larger step-like facets, creating a mesmerizing hall-of-mirrors effect.

Remember, each diamond shape has its own characteristics and unique beauty. It's important to try different shapes and see which one resonates with your style and preferences. Additionally, consider factors like diamond cut quality, color, clarity, and carat weight to ensure you select the perfect diamond for your engagement ring.