Fastness Testing

Part of Natural Dyes & Inks

Testing natural dyes for resistance to washing, light, rubbing, and perspiration.

Why This Matters

Producing a beautiful color is only half the job. The other half is making that color last. A dye that fades in the first week of sunlight or bleeds in the first wash is worse than no dye at all — it wastes precious dye materials, labor, and fiber. Fastness testing tells you, before you dye a large batch, whether a particular dye-mordant-fiber combination will hold up to the conditions it will face in actual use.

In a rebuilding context, you don’t have access to standardized laboratory testing equipment. But the fundamental tests — wash fastness, light fastness, rub fastness, and perspiration fastness — can all be performed with nothing more than water, soap, sunlight, and your hands. These simple tests, performed consistently, build a body of knowledge about which dyes are reliable and which are fugitive (prone to fading).

This knowledge determines what dyes you invest effort in cultivating, harvesting, and processing. It prevents the waste of dyeing an entire garment with a color that won’t survive a month of wear.

Types of Fastness

Wash Fastness

Resistance to color loss during washing. This is the most practically important test — textiles must be washed.

Rating	Description	Practical Meaning
Excellent	No color change after 10+ washes	Garment will maintain color for years
Good	Slight fading after 5-10 washes	Acceptable for most clothing
Moderate	Noticeable fading after 3-5 washes	Acceptable for items washed rarely
Poor	Significant fading after 1-2 washes	Unacceptable for clothing; decorative use only
Fugitive	Color washes out immediately	Not a true dye; just a stain

Light Fastness

Resistance to fading from exposure to sunlight (UV radiation). Critical for any textile used outdoors or near windows.

Rating	Description	Practical Meaning
Excellent	No visible fading after months of sun exposure	Suitable for outdoor use, curtains, awnings
Good	Slight fading after extended exposure	Normal clothing and indoor textiles
Moderate	Fading visible after 2-4 weeks of direct sun	Indoor use, stored away from windows
Poor	Fades significantly within days	Must be stored in dark; limited practical use

Rub Fastness (Crock Fastness)

Resistance to color transferring when rubbed against another surface. Important for clothing (especially where fabric rubs against skin or other fabrics) and for dyed materials that will be handled.

Perspiration Fastness

Resistance to color change or loss from contact with sweat. Particularly important for garments worn against the skin — undergarments, shirts, headwear.

Testing Methods

Wash Fastness Test

Equipment needed:

• Small samples of dyed fabric or yarn (at least 5 identical samples)
• Clean white fabric (undyed cotton or wool)
• Mild soap
• Warm water
• A way to record observations

Procedure:

1. Cut 5 identical samples from your dyed material — each about 50mm x 50mm, or 50cm of yarn.

2. Prepare wash solution — Dissolve a small amount of soap in warm water (40°C for wool, 60°C for cotton). Use about 5g of soap per liter.

3. Sandwich each dyed sample between two pieces of clean white fabric. Stitch or pin the sandwich together.

4. Wash the first sandwich — Submerge in soapy water and agitate gently for 30 minutes. This simulates one wash cycle.

5. Rinse in clean water and squeeze dry.

6. Evaluate:

   • Color change — Compare the washed sample to an unwashed sample. Note any fading, color shift, or uneven loss.
   • Staining — Examine the white fabric. Any color transfer indicates bleeding. Rate the severity.

7. Repeat — Wash the second sandwich twice (representing 2 wash cycles), the third sandwich three times, and so on.

8. Record results — Note the number of washes at which noticeable fading first occurs and the number at which the color becomes unacceptable.

Accelerated Testing

To simulate heavy use quickly, increase soap concentration and water temperature (within the fiber’s tolerance). This is harder on the dye and gives a conservative estimate of real-world performance.

Light Fastness Test

Equipment needed:

• Dyed sample cut in half
• A window or outdoor location with consistent sun exposure
• A way to cover half the sample

Procedure:

1. Prepare two identical samples from the same dyed batch.

2. Expose one to sunlight — Mount one sample in direct sunlight (south-facing window in the Northern Hemisphere, or outdoor location). Pin it to a board or frame.

3. Store the control — Keep the identical sample in a dark drawer or wrapped in opaque cloth.

4. Check weekly — Every 7 days, compare the exposed sample to the dark-stored control by placing them side by side in neutral indoor light.

5. Record observations — Note the week at which fading first becomes visible, and the week at which it becomes significant.

Alternative method (half-cover):

1. Take a single sample and cover exactly half of it with an opaque card or piece of wood
2. Expose to sunlight for a set period (2 weeks is a good starting point)
3. Remove the cover and compare the exposed half to the covered half
4. The covered half shows the original color; the exposed half shows the faded color

Interpreting Results:

Weeks to Noticeable Fade	Rating
8+ weeks	Excellent
4-8 weeks	Good
2-4 weeks	Moderate
Less than 2 weeks	Poor
Days	Fugitive

Rub Fastness Test

Procedure:

1. Cut a dyed sample and lay it flat on a firm surface.

2. Take a piece of clean white cotton and wrap it tightly around your finger.

3. Rub firmly across the dyed surface — 10 strokes back and forth with moderate pressure.

4. Examine the white cloth for color transfer.

5. Repeat with a damp white cloth — wet rub fastness is usually worse than dry rub fastness.

Rating:

Color Transfer	Rating
No visible color on white cloth	Excellent
Very faint trace	Good
Noticeable color	Moderate
Significant color	Poor
Heavy color transfer	Very poor

Perspiration Fastness Test

Procedure:

1. Prepare artificial perspiration — Dissolve 5g of salt (sodium chloride) in 1 liter of warm water. Add a splash of vinegar (to simulate the acidic pH of sweat, approximately pH 5-6). This approximates human perspiration.

2. Soak a dyed sample and a piece of white fabric together in this solution for 30 minutes.

3. Sandwich together — Place dyed and white samples in firm contact, press between two boards, and let sit for 4 hours at warm temperature (30-40°C ideally — body temperature simulation).

4. Separate and evaluate:

   • Color change on the dyed sample
   • Color transfer to the white fabric

5. Rate using the same scale as wash fastness.

Fastness of Common Natural Dyes

This table summarizes the typical fastness characteristics of well-mordanted natural dyes. Actual results depend on fiber type, mordant, and technique.

Dye Source	Wash Fastness	Light Fastness	Notes
Weld (Reseda luteola)	Good	Excellent	Best yellow for lightfastness
Madder (Rubia tinctorum)	Excellent	Good-Excellent	Improves with age
Indigo (Indigofera spp.)	Good-Excellent	Good	Rub fastness can be poor
Walnut (Juglans nigra)	Good	Excellent	No mordant needed
Oak gall + iron (black)	Good	Good	Iron can weaken fiber
Cochineal (Dactylopius coccus)	Good	Moderate-Good	Expensive but vivid
Onion skin (brown)	Good	Good	Easy and reliable
Marigold (Tagetes)	Moderate	Moderate	Not very lightfast
Turmeric	Poor	Very Poor	Fugitive — not recommended
Elderberry	Poor	Poor	Bleeds heavily; decorative only
Brazilwood	Moderate	Moderate	Fades toward pink
Logwood	Moderate-Good	Moderate	Better with chrome mordant (if available)
Pomegranate rind	Good	Good	High tannin content
Cutch (Acacia catechu)	Good-Excellent	Good	Traditional brown

Turmeric and Elderberry

These two are commonly cited as natural dyes but both are fugitive — they fade rapidly in light and wash out easily. They are stains, not true dyes. Avoid investing effort in dyeing with these unless the item will never be washed or exposed to light.

Building a Fastness Reference Library

Creating a Standard Sample Book

Over time, build a physical reference book of dyed samples with fastness data:

1. For each dye recipe, prepare 6 identical small samples (50mm x 50mm)

2. Label each sample with: dye source, mordant, fiber, date, and recipe details

3. Assign samples to tests:

   • Sample 1: Control (stored in the dark, unwashed)
   • Sample 2: Wash test series
   • Sample 3: Light exposure test
   • Sample 4: Rub test
   • Sample 5: Perspiration test
   • Sample 6: Reserve

4. Mount samples in a notebook or on cards with complete records

5. Update periodically — Re-examine light-exposed samples at intervals; add wash-test results as they accumulate

What to Record

Field	Purpose
Date dyed	Track long-term changes
Dye source + quantity (% WOG)	Reproducibility
Mordant + quantity	Reproducibility
Fiber type	Different fibers = different results
Wash fastness rating	After 1, 3, 5, 10 washes
Light fastness rating	After 2, 4, 8 weeks exposure
Rub fastness (dry/wet)	At time of dyeing
Perspiration fastness	At time of dyeing
Notes	Anything unusual or notable

Improving Poor Fastness

If testing reveals inadequate fastness, several interventions can help:

For Poor Wash Fastness

• Re-mordant and re-dye — The original mordanting may have been insufficient
• Tannin after-treatment — Soaking dyed fiber in a tannin bath (oak gall, sumac) can improve wash fastness for some dyes
• Increase mordant concentration — Try 15-20% WOG alum instead of 10-12%
• Extend mordanting time — Longer mordant soaks improve uptake

For Poor Light Fastness

• Choose different dyes — Some dyes are inherently fugitive. No amount of mordanting will make turmeric lightfast. Switch to weld, madder, or indigo for items that will see sun.
• UV-protective finish — A thin coat of linseed oil on dyed fabric provides some UV protection (though it changes the hand and appearance)
• Design around it — Use fugitive dyes only for items stored in the dark or replaced frequently

For Poor Rub Fastness

• Rinse more thoroughly — Surface dye causes most crocking. Extended rinsing removes loose dye.
• Vinegar rinse — A final rinse in acidulated water helps fix some dyes
• Reduce dye concentration — Heavily dyed fiber is more likely to crock because excess dye can’t all bond to the fiber
• For indigo — Rub fastness improves with more oxidation time between dips and thorough final rinsing

Practical Decision Framework

Use fastness testing to make practical decisions:

Intended Use	Minimum Fastness Required
Everyday clothing	Good wash + good light + good rub
Work clothing	Excellent wash + good rub
Outdoor textiles (awnings, flags)	Good light is essential
Bedding	Good wash + good perspiration
Decorative hangings (indoor)	Moderate wash + moderate light
Ceremonial items (stored, rarely used)	Any fastness acceptable
Trade goods	Excellent all-round — reputation depends on it