Acid Black 1 and Direct Black 22 are both black dyes, but they dye different fibres, so you read their spec sheets differently. Acid Black 1 is applied in an acid bath to wool, nylon, silk and leather. Direct Black 22 is applied to cellulosic fibres such as cotton and viscose, and to paper and leather.
Both are sold under their Colour Index names by many suppliers. The name identifies the dye family, not the strength, shade, salt content or fastness you will actually receive.
What the two dyes have in common
Several spec points apply to any black dye. Put each one in writing with a method and a tolerance:
- The C.I. name and the CAS number on the SDS, so you know which product is quoted. See the Colour Index number.
- Relative strength against a named standard, tested in a dyeing under set conditions. See dye strength measurement.
- Shade tolerance to the standard, with the colour-difference method named.
- Moisture and inorganic salt content, because they change how much real dye is in each kilo.
- Solubility in water at the temperature you will use, with no residue on a filter test.
Spec points for Acid Black 1
Acid dyes depend on the fibre taking up the dye evenly from an acid bath. Ask for levelness on your fibre, since nylon in particular can show streaks if the dye strikes too fast. State the fibre and the dyeing recipe that the supplier's test must use.
Check wash fastness and light fastness on the fibre you dye. If you use it on leather, ask for the leather-specific tests your customers require. Our guide on acid dyes explained covers the fibre side.
Spec points for Direct Black 22
Direct dyes are simple to apply but have modest wash fastness on their own. Many dyehouses add an after-treatment to improve it, so test fastness both with and without your usual fixing step. The supplier's figures may refer only to untreated dyeings.
For paper, ask about dusting and solubility, since undissolved particles cause spots. Read direct dyes explained for where each use fits.
Restricted substances and the COA
Black azo dyes are often covered by restricted-substance lists. Do not assume a dye complies. Ask for test evidence for banned arylamines and for the heavy metal limits in your customers' rules, and confirm with an accredited laboratory. Read banned amines and dye testing.
Each lot should come with a certificate of analysis showing the tests above. See tests on a dye COA for what to expect, and keep a retention sample of every lot.
Packing, storage and shelf life
Dyes are usually packed in fibre drums or bags with a plastic liner. Ask for the pack size, the net weight and the batch marking, so each drum traces back to a lot. Keep the dyes dry, sealed and away from heat, because moisture changes the weight of real dye and can cause caking.
Ask the supplier for a stated shelf life and the storage conditions behind it. Our guide on shelf life of dyes and pigments explains what to expect.
Next step
Decide your fibre and end use first, then write one specification for each dye. We find and audit dye makers, check samples and documents, and have lots tested. To compare suppliers of these dyes, book a free sourcing review.