You check batch-to-batch consistency by testing each lot against the same sealed standard, using the same methods every time, and comparing the results over many lots. A single pass or fail tells you little. A record of every lot shows whether the supplier is drifting.
Dye inconsistency is one of the most common causes of re-dyeing and shade complaints in textile mills. It also tends to appear after the first few orders, once the buyer stops watching closely. Read why quality drops after the first container.
What to measure on each lot
- Strength against the standard, by solution and by lab dyeing, as explained in how dye strength is measured.
- Shade against the standard, as a colour difference value under agreed light sources.
- Moisture content, since a damp lot weighs more and dyes weaker per kilogram.
- Solubility and insoluble matter, which affect spotting and filter blocking.
- Physical form, dust and flow, which affect automatic dispensing.
- Dyeing behaviour, such as exhaustion and fixation, for key reactive and disperse dyes.
How to set up the checks
First, agree one standard sample with the supplier. Split it, seal both halves, and keep one each. Record the date and lot number of the standard.
Second, ask for every lot's COA before shipment, with actual measured values, not only a pass statement. Compare the COA with your own incoming test on a retained sample.
Third, keep a simple table or chart of every lot's strength and colour difference. Over ten or twenty lots, you will see whether results scatter around the standard or move in one direction. Steady drift often means the supplier's own standard is changing, or that it has switched an intermediate or a blending component.
Fourth, run a bulk check now and then. Lab tests can pass while a lot still behaves differently in a full-scale machine. Ask your mill to record which dye lot went into each dyed batch, so that any shade problem can be traced back.
Warning signs
- Every COA shows exactly the same figures, which suggests the values are copied rather than measured.
- Strength is always at the bottom of the tolerance, which suggests the lot is being stretched with diluent.
- Shade passes in daylight but fails under shop lighting, which suggests a change in shading components.
- Lots arrive with different pack types or labels, which can mean the goods came from a different plant.
- The supplier is slow to send retained samples when you raise a complaint, or cannot find them.
Next step
Consistency needs someone watching every lot, not just the first. We hold your standard, check each lot's COA and sample before loading, and have independent tests done when results move. To set this up, book a free sourcing review.