A dye certificate of analysis should show the tests that predict how the lot will behave in your plant. At minimum, that means strength and shade against your standard, plus moisture, insoluble matter and solubility, with actual results for the exact lot shipped.
Some tests suit every dye. Others depend on the dye class and your process. Agree the list in your specification so every COA follows the same format. A common format also makes it easier to compare suppliers and to spot a lot that is out of line. For the basics of any chemical COA, read what a certificate of analysis is.
Identification details
- The product trade name and Colour Index name, matching your purchase order and invoice.
- The lot or batch number, matching the labels on the packs.
- The manufacturing date and the shelf life or retest date.
- The quantity covered by the certificate.
- The name of the person who approved the results, and the date.
Core tests for most dyes
- Strength as a percentage of the agreed standard, with the method and tolerance.
- Shade as a colour difference value against the standard, with the light sources used.
- Moisture content, usually measured by loss on drying.
- Insoluble matter, which shows how clean the dye is and how likely it is to spot.
- Solubility in water at a stated temperature, for soluble dye classes.
- The pH of a solution at a stated concentration.
Extra tests by dye class
Disperse dyes should also show dispersion stability, often through a filter test at dyeing temperature. Reactive dyes may show fixation or a hydrolysis check. Liquid dyes should show density, viscosity and solids. Granules may show dust level and particle size.
Some tests are better done less often by an outside laboratory. Banned amines, heavy metals and restricted substances are usually covered by periodic test reports rather than every COA. Ask for those reports on a fixed schedule, such as once a year per product, and whenever a raw material or production site changes. See how dyes are tested for banned amines.
Signs of a weak COA
- It says only pass, with no measured values or units.
- It lists a specification but not the method used.
- It carries no lot number, or a lot number that does not match the packs.
- It looks identical for every shipment, down to the decimal point.
- It is issued by a trader on its own letterhead with no link to the manufacturer's lot.
- The date of testing is after the shipping date, or long before the manufacturing date.
Next step
We review COAs before goods leave, compare them with retained samples and have lots tested independently when needed. To start, book a free sourcing review.