Matters arising regarding experimental release of elements from rock varnish by Black et al

The recent paper by Black et al. (npj HeritageScience 14, 90 (2026)) describes experimental weathering studies that are important to fundamental heritage science. The experimental method and results appear sound. However, the discussion relies on problematic statements and equivalences related to the experimental material, differences between field and laboratory conditions, evidence for long-term changes in field rock surface pH, and the role of the microbiome. Because of these issues, the conclusions of Black et al. must be considered speculative.