How to do a Shrinkage Test

I asked Jennifer Ennis to write a guest entry to elaborate on the comment she made under How to calculate denim shrinkage as a guest entry because a site search doesn't return results from comments (Timo's comment was also useful). She agreed and this is the result. Thanks Jenn!
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How to do a Shrinkage Test
Here's a little bit of a write up on how to perform a Shrink Test. It's good for either garment washed ' i.e. denim or testing home laundry conditions.

You can find more information on our web, so please take a look.

Supplies:

• It is best to create a good template for marking so that you're not measuring out squares over and over again ' preferably made from acrylic with a handle on one side to make it easier to hold. Or you can purchase a template from testing supply house.
• If you are using light colored fabrics, you can use a permanent marker like a 'Sharpie'. If you're testing a dark colour, look for metallic 'Artline Markers'. If you're washing with chemicals like enzymes or acids (for wash effects) do a test wash to see if the marking stays. There are also paint pens which cost $15 apiece but sharpies and artline markers are cheaper.

The process:

1. Draw a square on the fabric with interior dimensions of 12.5 inches aligned to the warp of the fabric with a permanent marker. Make sure the lines are dark and even in thickness.
2. Mark the warp direction with an arrow
3. If doing multiple squares across (good), number the squares and record these on your chart
4. Wash and dry the fabric
5. Do not press or iron the fabric, this will change the dimensions (you can do a separate test for pressing too, a good idea for dry clean only)
6. Measure the square in the weft direction in at least three places, from inside the line on one side to the inside of the line on the other side and record each measurement
7. Repeat measuring for the wrap (weft) direction

Calculation: (1/8' equals .125')
The easiest rule of thumb to remember is that for every 1/8' the lines shrink, this equals one percent in shrinkage.

• Ex. Before wash, the lines measured 12.5 inches so if the fabric measures 12 3/8' after wash, the difference is 1/8 or 1% shrinkage calculated as .125/12.5=0.01 x 100 = 1%
• Ex: If the fabric measures 12 1/4 inches after wash, the difference is 2/8 or 2% shrinkage, calculated as .250/12.5=0.02 x 100 = 2%
• Because each 1/8' less in line length equals one percent of fabric shrinkage, the lines are drawn (pre-wash) to the specific length of 12.5' to make math calculations unnecessary.

Below is a sample chart I recreated from memory that I used at a local garment manufacturer (full size).

The details one should record are standard, such as

• Fabric name (i.e. Black Streaky)
• Fabric code (CCBS11)
• Fiber content (i.e. 100% Cotton)
• Fabric supplier or source (Arvind Mills Ltd)
• Date
• Tester's name
• Batch or lot number (of the fabric)
• Colour (Denim)
• Wash details
  • water temp
  • duration
  • chemicals used (enzyme, detergents, bleach etc..)
  • dry temp and duration

Also see the previous entry Materials testing #/ which include full size forms with these details.

[Amended}
Jennifer forwards two additional thoughts:

1. If you are going to doing 5 home laundries, add columns to the table and keep remeasureing the same fabric. It's usually a good idea to touch up the lines if they start to fade (common if drawn in metallic marker).
2. Cut 3 inches away from the lines if you're cutting it out of your production header. This allows for raveling.

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