Basic Fabric Shrinkage and Colourfastness Testing

Hello! In the last lesson, you compared how swatches feel, hang, cover, and recover. Those observations describe fabric before care. Now you’ll find out what happens when water and washing are involved: does the fabric change size, and does its colour transfer? Both matter before cutting a garment that must keep its fit and appearance.

This lesson takes about 40 minutes of study and hands-on work. A colour-transfer check includes a 30-minute soak that can run while you read and prepare the shrinkage test. The shrinkage measurement must wait until its swatch is completely dry, which may mean finishing that entry later.

Two questions, two tests

Shrinkage is a change in dimensions after care. Colourfastness describes how well colour resists change or transfer under particular conditions. A fabric might retain its dimensions yet stain a pale lining, or keep its colour yet shorten enough to affect the fit of trousers.

Watch two short passages from Evelyn Wood’s How to Pre-Wash Your Fabric Before Sewing in 4 Steps. They establish the guiding principle for both checks: test using the care routine the finished garment will actually receive.

Check any care instructions before you begin. If the intended fabric is dry-clean-only, do not treat a home water test as a prediction of dry-cleaning performance. You can test a spare scrap to learn how it reacts to water, but do not assume the garment can then be washed.

For a washable fabric, gather a ruler, a fabric marker or thread for marking, the detergent you expect to use, a bowl, a clean white cotton scrap, and three pieces from the same fabric: one large enough to measure, one small piece for soaking, and a third for rubbing. Keep an unwashed offcut as a colour reference. Test one coloured fabric at a time; do not put an unknown dye in with other laundry.

Measure shrinkage in both directions

Recall the lengthwise and crosswise directions you located earlier. They can shrink by different amounts, so one measurement is not enough. Read EYSAN FABRICS’ What Is Fabric Shrinkage?, concentrating on its home procedure and calculation rather than its laboratory methods.

For a manageable home test, cut a swatch roughly 25 cm by 25 cm if you have enough fabric. Mark four small crosses inside it so the distance between marks is 20 cm lengthwise and 20 cm crosswise. Leave a margin around the marks: measuring between marks is more dependable than measuring edges that may fray. If you have only a smaller swatch, use shorter marked distances and record them accurately; a small measuring error will then have a greater effect on your percentage.

Write down both distances before washing. Wash and dry the swatch according to the intended garment-care routine, without mixing it with pale items. Once it is fully dry, lay it flat without pulling or smoothing it into a larger shape. Measure between the same pairs of crosses.

For each direction, calculate:

For example, if the lengthwise marks were 20 cm apart before washing and 19.2 cm apart afterward, lengthwise shrinkage is $4\%$. If the crosswise distance changes from 20 cm to 19.8 cm, crosswise shrinkage is $1\%$. Record the two results separately. A negative result with this formula means the fabric grew, rather than shrank. This differs in sign from the reading’s after minus before formula; the underlying measurements are the same.

A home test does not establish a permanent shrinkage rate. Another wash or a different drying method could produce a different result. It does give you evidence for deciding whether and how to pre-treat fabric before cutting.

Check where the colour goes

Colour in the water and colour staining another fabric are related observations, but they are not identical. Read the home-test sections of Color Fastness Testing: A Quilter’s Guide to No-Bleed Fabric. Although its examples concern quilts, the light-against-dark problem also matters for a top with pale trim or a kameez with a light lining.

Begin the soak test now if you have not already. Place one coloured scrap and a clean white cotton scrap together in a clear jar or pale bowl with enough water to cover them. Use a water temperature permitted by the fabric’s care instructions. Leave them for 30 minutes, noting the temperature and whether you used detergent; adding your intended detergent makes this a different, potentially more revealing home check than the guide’s water-only soak. While they soak, you can mark and wash your shrinkage swatch.

After 30 minutes, note the water’s appearance, then remove and inspect the white scrap. Has it remained white, picked up a faint tint, or stained visibly? Compare the coloured scrap with your unwashed offcut after both are dry, under the same light, to check for colour change. Wet fabric can look darker even when no lasting colour change has occurred.

For a wet-rub check, dampen a fresh area of white cotton with water. Press it against a separate coloured scrap and rub back and forth several times with consistent, firm pressure. Inspect the white cloth immediately. This tests surface transfer during rubbing, not just dye release during soaking.

In the pre-washing video, Wood also demonstrates a quick blotting check on a multicoloured fabric:

The image below shows how a light fabric can be placed in contact with coloured samples for comparison. It shows the test setup, not a proven result: the samples would need to be examined after testing for staining.

Make the result useful later

A statement such as “colour is fine” leaves out the conditions under which you checked it. Keep a compact record for each fabric, including results that are uncertain or not yet measured:

For instance, “water lightly tinted; white cotton visibly pink; wet rub left a trace” is more useful than “poor fastness.” Visible staining is a warning if that fabric will sit beside a pale panel, lining, or garment. A clear test is encouraging, not a guarantee against transfer in every wash, at every temperature, or after wear. If you pre-wash a bleeding fabric, repeat the relevant check before deciding it is safe to combine with lighter materials.

Key takeaways

Test shrinkage by marking, measuring, caring for, fully drying, and remeasuring a swatch in both directions. Test colour behaviour by checking soak water, adjacent white fabric, wet-rub transfer, and any change in the coloured swatch itself. Record the care conditions alongside the results so you can use them when preparing yardage and making design decisions.

Next, you’ll connect these observations with the properties and typical uses of fabrics for tops, trousers, salwar kameez, and sari blouses.