How does negative staining help us visualize capsules?

Negative staining helps us visualize capsules by staining the background surrounding the capsule while leaving the capsule itself unstained. Negative staining uses acidic dyes, which have a negative charge. The negatively charged dye is repelled by the negatively charged bacterial capsules, preventing it from penetrating the capsule and dyeing the cell. Instead, the dye stains the background only so it appears as a dark halo around the borders of the clear unstained capsule. The advantage of negative staining is that it provides a clear contrast, making it easier to visualize and measure the bacterial capsule.