To enhance the contrast and protect your laser-engraved slate, follow these steps:

1. Choose the Right Finish: After engraving, select a suitable finish that will enhance the contrast. Acrylic spray sealants or matte finishes can help bring out the details in the engraving.
2. Apply a Cleaning Solution: Before finishing, clean the slate surface with a gentle cleaning solution to remove any dust or debris that may diminish contrast. Use a soft cloth to avoid scratches.
3. Use a Color Filler: For added contrast, consider applying a color filler. Choose a paint or epoxy resin that contrasts well with the slate color. Carefully fill the engraved areas and wipe off excess for a clean look.
4. Seal the Surface: Once the filler is dry, apply a protective sealant designed for stone surfaces. This will help prevent moisture damage and fading from UV exposure.
5. Regular Maintenance: Clean the slate regularly with a soft cloth and mild detergent to maintain its appearance. Avoid abrasive cleaners that can scratch the surface.

By following these steps, you can improve the visibility of your engraving while ensuring its longevity.