Indigo Vat Calculator

The calculator doesn't know which vat chemistry you're running, so you set the ratios directly: a classic 1-2-3 fructose/lime vat runs about 3 parts reducing agent (fructose) and 2 parts alkali (calcium hydroxide) per part indigo, a sodium hydrosulfite vat typically needs a somewhat lower reducer ratio with a similar alkali ratio, and an iron (ferrous sulfate) vat runs close to 3:2. Match the ratio inputs to whichever recipe you're actually mixing, since plugging in the wrong vat's ratios will size your reducing agent and alkali incorrectly even though the indigo weight itself stays correct.

Indigo needed is driven entirely by fabric weight and your target % OWF, and reducing agent and alkali are each a fixed ratio of that indigo weight — none of those three depend on vat volume at all. Vat volume only feeds into one separate output, indigo concentration in grams per liter, which tells you how strong the vat solution is once you've decided how much total liquid to use; a smaller vat volume for the same indigo charge produces a more concentrated vat, not a different amount of chemicals.

It's your target % OWF divided by 1.5 and rounded to the nearest whole dip, based on the rule of thumb that a well-maintained vat deposits roughly 1.5% OWF per dip-and-oxidize cycle — so a 6% target suggests about four dips. Real vats vary: a fresh, strongly reduced vat can deposit more indigo per dip while a tired or under-reduced vat deposits less, so treat this as a planning estimate and judge actual depth by checking the fabric's oxidized color between dips rather than stopping at a fixed dip count.

The alkali ratio input is generic — it represents whichever alkali your vat recipe calls for, whether that's calcium hydroxide (lime) in a fructose vat, soda ash in a hydrosulfite vat, or lye in some formulations. The calculator only computes a weight in grams from your ratio; it doesn't distinguish between alkali chemistries or adjust for their different strengths, so you still need to use the ratio appropriate to the specific alkali named in your chosen vat recipe.