What does the process of 'Boxing' refer to in paint mixing?

The process of 'Boxing' in paint mixing primarily involves pouring paint from one container to another to achieve complete mixing. This technique is essential to ensure uniformity in the paint's color and consistency, especially when dealing with materials that may have been manufactured in batches. By transferring paint between containers, any pigment settling can be reintroduced, leading to a more homogeneous mixture. This practice is critical in preventing variations in color that can occur if paint from different containers is applied separately.

The other options, while relevant to the broader context of painting, do not accurately describe what 'Boxing' entails. Applying multiple layers of paint relates to the painting process rather than the mixing phase. Testing paint adhesion focuses on how well paint adheres to a surface, which is vital for performance but not its mixing. Preparing surface areas is also a crucial step before painting but does not involve the mixing of paint itself.