Discharge Printing Calculator
Chemical concentration for color removal printing.
About this calculator
Discharge printing works backwards from most dyeing: instead of adding color, you print a paste containing a reducing agent onto already-dyed fabric to chemically destroy the ground dye wherever the paste touches, leaving white or (with an added illuminating dye) a new color printed into the dark ground. This calculator first sizes the batch by multiplying your print area by a paste pickup rate — the weight of paste deposited per square meter, which varies by application method (flat screen 80-120 g/m², rotary screen 60-100 g/m² since it applies less pressure, hand block 100-150 g/m² because manual pressure is less consistent and needs a thicker deposit). From that total paste weight, it works out the discharging agent, thickener, and alkali as grams per kilogram of paste, each converted from the "per kg" dosage you specify to an absolute weight for your batch.
Water is calculated as whatever's left over once those three chemical weights are subtracted from the total paste weight, treating the paste as chemicals-plus-water with no separate allowance for the illuminating dye itself. The most common chemical here, zinc formaldehyde sulfoxylate (sold as Rongalit C), is a reducing agent that breaks the chemical bonds holding the ground dye's color; the alkali (caustic soda or soda ash) activates that reduction, and the sodium alginate thickener keeps the paste from bleeding into fabric it shouldn't touch. Because discharge chemistry only works against dischargeable dye classes — it won't remove pigment prints or discharge-resistant reactive dyes — always test a swatch of your actual ground-dyed fabric before committing to a full print run.
Inputs
Results
Total paste needed (g)
1,000
How to Use This Calculator
- Enter Print area (m²), Paste pickup (g/m²), and Discharging agent (g/kg paste).
- Set Thickener (g/kg paste) and Alkali (g/kg paste).
- Review the Total paste needed (g) result.
- Use Discharging agent (g) and Thickener (g) to inform your decision.
How the result changes with Print area (m²)
| Print area (m²) | Total paste needed (g) |
|---|---|
| 5 | 500 |
| 7.5 | 750 |
| 15 | 1,500 |
| 25 | 2,500 |
What each input means
- Print area (m²)
- Total fabric area to be printed with discharge paste.
- Paste pickup (g/m²)
- Paste applied per m². Flat screen: 80-120, rotary: 60-100, hand block: 100-150.
- Discharging agent (g/kg paste)
- Zinc formaldehyde sulfoxylate (ZFS) concentration. Typical: 50-150 g/kg.
- Thickener (g/kg paste)
- Sodium alginate or guar thickener. Typical: 30-60 g/kg.
- Alkali (g/kg paste)
- NaOH or sodium carbonate. Typical: 10-30 g/kg.
What each result means
- Total paste needed (g)
- Total weight of print paste to prepare.
- Discharging agent (g)
- Weight of reducing agent (ZFS/Rongalit C).
- Thickener (g)
- Weight of sodium alginate or guar thickener.
- Alkali (g)
- Weight of sodium hydroxide or soda ash.
- Water (g)
- Water to add to complete the paste.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersPrint area (m²) = 10, Paste pickup (g/m²) = 100, Discharging agent (g/kg paste) = 100, Thickener (g/kg paste) = 40 = 5 input(s) provided
- Calculate Total paste neededTotal paste needed = printAreaM2 * pastePickupGPerM21000 = 1000
- Calculate Discharging agentDischarging agent = totalPasteKg * dischargingAgentGPerKg100 = 100
- Calculate ThickenerThickener = totalPasteKg * thickenerGPerKg40 = 40
Engine last updated . Checked against 1 independently-derived test — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does changing the print method (flat screen vs. rotary vs. hand block) change the total paste needed?
Total paste is printAreaM2 × pastePickupGPerM2, and pastePickupGPerM2 is set directly by your application method. Rotary screens apply less pressure and deposit only 60-100 g/m², flat screens run 80-120 g/m², and hand block printing needs 100-150 g/m² because manual pressure is less consistent and needs a thicker paste deposit to compensate.
Why might the Water output come out as zero?
Water is calculated as totalPasteG minus the sum of discharging agent, thickener, and alkali weights, floored at zero by Math.max(0, ...). If your per-kg chemical dosages are set high enough that their combined weight equals or exceeds the total paste weight, the model has no room left for water and reports zero rather than a negative number.
What's the difference between the discharging agent and the alkali in this recipe?
The discharging agent (typically zinc formaldehyde sulfoxylate, sold as Rongalit C) is the reducing chemical that actually breaks down the ground dye's color. The alkali — caustic soda or soda ash — activates that reduction reaction; without it, the discharging agent is far less effective at destroying the dye even at the same concentration.
Will this recipe work on any pre-dyed fabric?
Not necessarily — discharge chemistry only removes dischargeable dye classes, and it won't touch pigment prints or discharge-resistant reactive dyes regardless of how much reducing agent or alkali you calculate here. Always test the actual ground-dyed fabric with a small swatch before committing chemicals and time to a full print run.
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