Two test methods that decide whether a galvanizing certificate means anything. What each one measures, and what a buyer should ask to see.
IS 6745 is the method for determining how much zinc is on the article — the specimen is weighed, the coating dissolved in inhibited acid, and the specimen reweighed. The difference, divided by the surface area, gives the coating mass in g/m² directly. It is the referee method behind every IS 4759 figure.
IS 2633 is the method for testing whether that zinc is evenly distributed — the copper sulphate (Preece) dip. A mass average can pass comfortably while a corner or a weld toe is thin, and the dip test is what catches it.
| IS 6745 | IS 2633 | |
|---|---|---|
| Measures | Mass of zinc per unit area | Uniformity and continuity of the coating |
| Method | Strip the coating in inhibited acid, weigh before and after | Repeated dips in standard copper sulphate solution |
| Result | A number in g/m² | Pass or fail at a stated number of dips |
| Destructive | Yes — run on a specimen or a sample piece | Yes — run on a specimen |
| Catches | A coating that is too light overall | A thin or bare spot that an average would hide |
| Does not catch | An uneven coating that averages correctly | A coating that is uniform but uniformly thin |
The two are complementary, which is why IS 4759 references both. A certificate quoting one and not the other has told you half the story.
Four questions that separate a real report from a formality.
Answered from our own line, not from the standard's cover page.
The copper sulphate dip test standardised in IS 2633. A specimen is dipped repeatedly in a standard copper sulphate solution; where the zinc is thin or absent, copper plates out as a bright adherent deposit. It is a uniformity check, not a thickness measurement.
Because the standard and the instrument disagree on units. IS 4759 states the requirement as coating mass in g/m²; a DFT gauge reads thickness in microns. At roughly 7.14 g/m² per micron the two convert cleanly, so both belong on the report.
No — both are destructive. They are run on specimens or sample pieces. The parts themselves are checked with a calibrated DFT gauge, which is non-destructive and can be read at many points.
Yes. In-house we run a Bruker Q2 ION optical emission spectrometer imported from Germany and commissioned in June 2026, reading steel, zinc, aluminium and copper; a universal testing machine; an analogue Rockwell hardness tester; and calibrated DFT gauges. We also run an in-house tool room.
Yes, at your cost, and we would rather you did. Inspection by SGS, Bureau Veritas, TÜV, DNV, Intertek or your own nominated agency is supported.
Tell us the standard, the coating requirement and the component, and we will confirm in writing what we can hold and how we will certify it. Galvanizing is on our own floor, so the answer comes from us and not from a sub-contractor.
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