Dye Recipe · How to Mordant Linen · Indigo dyeing · traditional methods · Aug 11, 2025

Potash vs. Soda Ash – Which Alkali Should You Choose for Natural Dyeing?

If you’ve bought “Soda Ash” from us in the past, you were actually using Potash (Potassium Carbonate) – and it’s time to set the record straight! We’ve now updated our labelling so you know exactly what you’re getting.

While Potash and Soda Ash are both alkaline powders that raise pH and are essential in many dyeing processes, they are not the same substance. Knowing the difference will help you choose the right one for your project.

The Chemistry in Brief

Name	Chemical formula	Alkali strength	Common source	Other names you might know
Potash	K₂CO₃	Stronger alkali	Traditionally from wood ash, now refined industrially	Pearl ash, potassium carbonate
Soda Ash	Na₂CO₃	Slightly weaker alkali	Traditionally from plant ash, now from sodium-rich minerals	Washing soda, sodium carbonate

How They Work in Natural Dyeing

Both Potash and Soda Ash:

Raise the pH of dye baths.
Are used to scour cellulose fibres (cotton, linen, hemp, bamboo).
Help intensify certain plant dyes (e.g. weld yellow).
Adjust the pH of indigo and woad vats.

Potash – Potassium Carbonate

Higher alkalinity than Soda Ash – works faster for pH adjustments.
Excellent for fructose and henna indigo vats – many dyers prefer it over sodium carbonate.
Dissolves easily in water.
Can give slightly brighter weld yellows when used in the final rinse or pH shift.
Traditionally made from wood ash; now available in a consistent, purified form.

Soda Ash – Sodium Carbonate

Slightly milder alkali than Potash – still effective, but gentler on fibres.
Works well for scouring cellulose fibres and in indigo vats where a slower pH rise is desired.
Often used in synthetic fibre-reactive dyeing as well as some natural dye processes.

Which Should You Use?

For most natural dyers:

Indigo & woad vats – Potash is an excellent choice, especially for fructose vats.
Scouring cellulose fibres – Either works; Potash acts faster, Soda Ash is gentler on finer threads.
Shifting colours with pH – Potash has a more pronounced effect.
Following historical recipes – Many traditional methods that mention “Potash” really mean potassium carbonate, not sodium carbonate.

About Our Labelling Update

If you purchased “Soda Ash” from us in the past, it was actually Potash (Potassium Carbonate). This mix-up is common in the textile industry, but we’ve now corrected our labels so you can choose with confidence:

Old listing name: Soda Ash – pH Adjuster & Scouring Agent
Correct chemical: Potash (Potassium Carbonate)
New listing name: Potash – Potassium Carbonate

We now also stock true Soda Ash – Sodium Carbonate so you can select the best alkali for your dye work.

Quick Reference: Potash vs. Soda Ash

Need a quick, strong pH rise? → Potash.
Want a slower, gentler shift? → Soda Ash.
Fructose or henna vat? → Potash.
Gentle scouring of delicate cellulose fibres? → Soda Ash.

💡 Tip: Potash’s higher alkalinity means you may need a little less than Soda Ash to achieve the same pH. Always measure carefully.