A texture grade is a starting point, not a specification. The same grade etched five microns deeper, the same tool running a different resin, a ten degree difference in mould temperature, and the gloss has already moved two to five GU. That is why we write three numbers into the drawing instead of one: the grade, the etch depth range, and the gloss range.
The grade describes pattern, the depth describes gloss. Each grade refers to a standard plaque that fixes the shape and density of the pattern. What actually decides how the surface reflects light is how deep the etchant cut: the same grade can be etched at 12 microns or at 22 microns, and one comes out bright while the other comes out flat. Etch depth of 10-25 microns corresponds to a surface roughness Ra of roughly 1.0-3.0 microns. Gloss is measured at 60 degrees, and with the same grade but a different depth the reading can differ by more than 5 GU. Suppliers quote by grade and produce by depth; if nobody reconciles the two in between, the answer only arrives at the first sample.
A line on our drawings reads: MT11010, depth 15-18 microns, gloss 3-5 GU. Three lines and the toolmaker, the etcher and the inspector finally share one language. Projects that specify only the grade routinely ship a second batch two gloss steps away from the first.
Resin changes the result as well. The texture is a field of pits in the tool, and the melt has to flow into them to replicate it. A resin with good flow reaches the bottom of the pits, so the texture looks shallower and reflects more; a resin with poor flow never fills them, so the texture looks deeper and flatter. PC is more viscous than ABS, and at the same grade a PC part usually reads brighter than an ABS part. Same tool, same grade, different resin: ABS 3.5 GU, PC+ABS 5.2 GU, PC 6.8 GU.
The real risk sits in batch consistency. On one housing a flame retardancy requirement forced a change from ABS to PC/ABS during the structural review. The grade was left untouched, and the first batch came back with the client saying it had lost the premium feel of the previous version. We had to re-etch and deepen by 4 microns to recover it. Changing resin means re-confirming the texture, not just swapping the material code.
Sampling is where texture is actually locked. A plaque rarely matches the real part, especially in dark colours: the plaque is flat and has no curvature, while the part is curved, and the same texture reflects differently at different curvatures. The workable method is a trial piece in the same resin and the same colour, etched to the planned grade and depth, judged under the lighting the product will actually live in. It costs very little time and prevents a whole batch from being reworked.
The order of etching matters too. Texture can be added but not removed: a shallow texture can be etched deeper, while a deep one can only be polished off that area and re-etched, and polishing changes flatness and edge sharpness. So we run the first batch deliberately shallow, keeping margin to deepen once the sample is approved. Starting deep and coming back usually means a new insert.
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