Mordants and Shades for Silk and Wool Dyed with Lac
Lac dye is one of the oldest natural reds of the Indian subcontinent. Here is how dyers use it on silk and wool, which mordants shape the shade, and what to put on a bulk order.
What lac dye is
Lac dye is the red colouring matter of the lac insect, a group of water-soluble anthraquinone compounds called laccaic acids (Colour Index: C.I. Natural Red 25). It is recovered from the wash water when raw sticklac is crushed and washed to make seedlac, then purified and dried to a dark red-brown powder. It was used on silk and wool in India and across Asia for centuries before synthetic reds, and it is chemically related to, but not the same as, cochineal.
Fibres and shades
Like most natural dyes, lac dye needs a mordant to fix it to the fibre. The fibre and the mordant together set the shade:
| Silk | Takes lac dye well · crimson to rose reds with an alum mordant |
| Wool | Deep crimson with alum · the classic carpet and shawl red |
| Iron after-bath | Shifts reds towards plum, purple and brown |
| Cotton and other cellulose fibres | Weaker uptake · usually needs a tannin step before alum, and gives lighter pinks and reds |
Mordants and the dye bath
- Alum (potassium aluminium sulphate) is the standard mordant for lac dye on protein fibres and gives the clearest reds.
- Iron is used as a light after-bath to darken and dull the shade.
- pH matters: laccaic acids are redder in a mildly acidic bath and turn more purple as the bath becomes alkaline, so keep the bath pH steady from lot to lot.
- Water: hard water and dissolved iron change the shade. Dyers working to a colour standard often use softened or filtered water.
Mordant and dye quantities depend on your fibre, depth of shade and process, so run a trial on your own material before a production lot.
Who buys lac dye
Natural-fashion and slow-fashion labels, artisan dye houses, carpet and shawl weavers, heritage textile restorers, craft and natural-ink makers, and laboratories studying bio-based colourants. Lac dye is not carmine (E120) and has no EU food additive number; for cosmetic colour use, the rules of your market apply — see shellac and lac products for cosmetics.
What to put on the specification
Ask for dye content with the test method, moisture, colour and solubility on the batch COA, and dye a trial skein from the sample lot before you order. Natural dye strength varies between lots, so state the shade standard you match to and ask for a fresh sample if you change supplier.
How we supply dyers
As a red lac dye supplier, we offer lac dye powder at ₹8,000 per kg, MOQ 25 kg, in 25 kg HDPE-lined bags or 5 kg pouches on request, with a batch COA. Samples of 100–500 g are available before the first order. We ship FOB Kolkata, CFR or CIF, and to Bangladesh by road through Petrapole–Benapole (HS 3203 00 30). Read how shellac is made to see where lac dye comes from in the chain.
Quick answers
Which mordant works best with lac dye? Alum is the standard mordant for silk and wool and gives the clearest crimson reds. A light iron after-bath shifts the shade towards purple and brown.
Can lac dye be used on cotton? Yes, but uptake is weaker than on silk or wool. Cotton usually needs a tannin treatment before the alum mordant and gives lighter pinks and reds.
Why does my lac dye bath turn purple? Laccaic acids are pH-sensitive. A bath that drifts towards alkaline, or hard and iron-rich water, pushes the colour from red to purple; keep the bath mildly acidic and use softened water.
This guide summarises publicly available information and industry practice as of October 2026. Run your own trials and check the rules for your market before ordering. It is not legal advice.
Dyeing with Natural Reds?
Lac dye at ₹8,000 per kg, MOQ 25 kg. Batch COA with every lot, sample before your first order.