Natural stone contains mineral grains, veins, pores, fossils and weathered zones that are part of the material. Color measurement is most useful when it characterises the approved distribution and supports sorting or matching—not when one reading is treated as the color of an entire slab.
Define the stone and the decision
Record stone type, quarry and bench, lot, slab, cut direction and surface finish. Decide whether the task is quarry or supplier comparison, slab selection, panel grouping, installed matching or weathering assessment. A range intended for expressive variation needs different rules from a nominally uniform façade or tile.
Control finish, moisture and treatment
- Compare polished with polished, honed with honed and flamed with flamed.
- Define dry conditioning; damp stone can darken and may exaggerate saturation.
- Record impregnator, enhancer, sealer or wax and its cure interval.
- Clean dust and slurry residue without changing the polish.
- Mark face and orientation where veining or grain direction affects appearance.
Wet-look approval is a separate method
If stone is intentionally evaluated wet or after an enhancer, specify that condition and use the same treatment on standard and sample. Do not compare it with an untreated dry master.
Plan a grid that represents the slab or batch
Photograph or map the specimen and define a grid or stratified sampling plan across field, vein and known feature zones. Measure several slabs across the lot. Retain location values, mean, range and distribution. For installed panels, preserve panel IDs and orientation so color data can support layout decisions.
Choose geometry and aperture
Use the largest practical aperture to average mineral grains, while avoiding mixing a named vein zone with the field unintentionally. SCI can reduce some polish influence; SCE is more sensitive to the finished appearance. On coarse, cleft or flamed stone, stable contact and multiple readings are essential. Measure gloss separately when polish is specified.
Set selection and matching rules
Define acceptable distribution, outlier treatment and adjacency rules from approved stone. Two panels may each lie within a broad master range yet clash when installed together. Pair overall lot limits with local grouping or sequencing where adjacent appearance matters. Use visual review at the intended scale and distance because a small aperture cannot describe veining layout.
Do not apply a universal Delta E limit across stone types. Establish the formula and boundaries using project samples and a measurement system capable of separating real variation from repositioning noise.
References and further reading
- ASTM E1164: object-color spectrometric data.
- ASTM E1345: multiple measurements for variable color.
- Averaging and repeatability.
Continue with textured building materials and architectural tolerances.
Last reviewed 22/09/2026 · Level: Intermediate
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