Dye strength is the amount of colour a dye gives compared with a reference standard. It is stated as a percentage, so a lot at 102% gives slightly more colour than the standard, and a lot at 95% gives less.
Strength matters because you pay by the kilogram but dye by colour. A lot that is a few percent weak means your mill uses more dye for the same shade, or misses the shade altogether.
Why dyes are standardised
Raw dye from the reactor varies in strength from batch to batch. Makers blend it with a diluent, such as salt, sodium sulphate or dextrin, to bring every lot to the same strength. This is called standardisation.
Many dyes are sold with a strength label such as 100%, 150% or 200%. These figures are relative to the maker's own reference, not to a pure dye. A 200% product from one supplier is not necessarily twice as strong as a 100% product from another. Always compare against your own standard.
How strength is measured
- Solution strength is measured with a spectrophotometer. The lab dissolves the dye and the standard at the same concentration and compares how much light each absorbs at the peak wavelength.
- Dyeing strength is measured by dyeing fabric or yarn with the lot and the standard under the same conditions, then comparing the colour with a reflectance spectrophotometer.
- Build-up tests dye at several depths to check the lot behaves like the standard in pale, medium and dark shades.
Which test to rely on
Solution strength is quick and repeatable, so it suits incoming checks. Dyeing strength tells you what will happen in your mill, because it includes how much dye actually goes onto the fibre. Some lots match in solution but dye weaker, for example if part of a reactive dye has hydrolysed in storage.
Agree in the contract which method decides acceptance, which standard sample is used, and what tolerance applies. Many buyers accept a narrow band of a few percent either side of 100%, and reject or adjust the quantity outside it. Put the method and tolerance in your dye specification, and ask for the result on every dye COA.
Keeping the standard honest
Your standard sample is only useful if it does not change. Store it sealed, dry and cool, and keep a second sealed portion untouched. Replace it on a fixed schedule with a lot both sides agree on. If a dispute arises, an independent lab can test the lot against the sealed standard.
Next step
We hold reference samples for you, check strength on each lot against them and have lots tested by an independent laboratory before they ship. To set this up, book a free sourcing review.