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A Guide to Understanding Fabric Grain

This is Part Two in a series pertaining to Quality Sewing, starting with some basics and slowly working on up.

Part One: "How Do You Measure Up?" A 'How To' on obtaining accurate measurements for sewing, commissioning, and buying

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"What Do Vegetarian Zombies Eat?"
A Guide to Understanding and Working With Fabric Grain

When you put together a garment that's been cut off-grain, any stitching on the garment can make the whole thing look wrong, regardless of whether it's been stitched correctly or not.
But, what exactly is the grain? How can we avoid cutting fabrics off-grain? How do we fix a fabric that's been warped?

What is "the grain?"
Grain, or grain-line, refers to the orientation of the yarns in a woven fabric.
In a weaving loom, the “warp yarns” run front-to-back to form your lengthwise grain (aka: “straight grain”).
The “weft yarns” (perpendicular to the selvage) are woven from side to side, through the warp yarns, and form your crosswise grain (aka: "cross-grain").
These should be perfectly perpendicular to each other when in the loom.

 What is "the bias?"
Bias is typically thought of as the exact 45º diagonal across the warp and weft yarns. While this is technically the “true bias,” bias can also refer to any angle along the straight or cross-grain. Basically, anything that isn't perfectly lined up with either the weft or the warp yarns.
Bias does have its place in certain patterns (because of its stretch and natural distortion, it provides beautiful draping), but it requires a lot of special effort during the cutting and construction process to ensure that you avoid the “wrong” kind of distortion. If you don't know how to work with fabric that's been cut on the bias, it can pull your fibers off-grain, and produce that strange appearance that just won't look right no matter what you do. For right now, we'll avoid working on the bias.

How do I line up with the grain?
If you're working with a commercial pattern, your (lengthwise) grain-line should be clearly marked with an arrow. This arrow should run parallel to the selvage edges (therefore: parallel to the warp yarns/straight grain) when you're laying your pattern piece. Looking at your fabric, you should be able to see how the threads are laid out, and follow them through the weave.
If you cannot see the weave very well, or are uneasy about the line you're following, don't be afraid to lightly tug a thread outside of where you're placing your pattern piece, and use it as a reference to line your pattern parallel to it.
If you're making your own pattern, or your grain-lines are not marked, then you should line up your pattern piece to allow maximum ease around the body, not lengthwise. The cross-grain (which, as we remember, is perpendicular to the selvage) has the most stretch, and therefore naturally has ease as the yarns flex during movement.
  • It's not impossible to make a wearable garment with the cross-grain running vertically, but as the fabric relaxes, the yarns will droop, and lengthen the garment.

Off-Grain
After a fabric has been woven, there are multiple points during the manufacturing steps (folding, rolling it onto the bolt), and after it reaches the fabric store (being unrolled and re-rolled onto the bolt, being pulled off the shelf to look at, tugged and prodded at by curious shoppers, etc), when the yarns can be pulled out of the proper square (aka: off-grain). This is exactly why it's important to follow the actual grain in the fabric, and tear along the grain whenever possible.
If you're working with any pattern piece that isn't a perfect rectangle, the grain should be straightened prior to any cutting. At the lengthwise edge of your fabric, snip the selvage, and pull one or two cross-grain threads to until you have a visible line to use as a stitching guide. Once you've cut along this edge, match the selvages and fold the fabric in half (ignore the fold already in the fabric). If the newly cut edge does not line up, your fabric is off-grain.

How do I get an off-grain fabric back on-grain?
The process of straightening out the grain is known as “squaring.” This is normally pretty easy to do (in theory), especially with the cotton fabrics typically used with Lolita garments. Some fabric finishes, however, are more resistant to this process than others, so I suggest pre-washing or steaming your fabrics to soften the yarns, and make them easier to square.
Once the yarns have been softened, all you have to do it hold the fabric at opposite diagonal corners and gently, gently tug. Clearly, you want to pull opposite of the current distortion, to get the yarns back to proper right-angles, and make the fabric look like a rectangle/square.
When you feel that you're getting close, fold the fabric to check your progress, and see how the edges (selvage and cross-grain) match up, and if necessary, steam and resume the tugging.
When the fabric has been squared, it should be pressed, following the lengthwise grain only. Remember, the cross-grain has natural stretch, and pressing in this direction may re-distort the fabric you just painstakingly squared. Trust me. It's not fun to re-fix it.

How do I cut on the grain?
To get a real cross-grain cut on a woven fabric, one should scissor through the selvage, and then tear the remainder of the fabric whenever possible.
  • Note! The easiest place to practice this would be on your Lolita-staple rectangle skirt pattern.
Why Tearing?
  • Tearing is faster than cutting, and more accurate when working with a straight line, and it will ensure that the piece will be perfectly on-grain.
When tearing, always, always, always do so quickly. It may seem intimidating, but tearing slowly will pull more along the torn edge, and therefore can fully distort parts of your weave.
In regard to delicate fabrics, tearing should be avoided altogether, because of the level of risk involved. However, because it's also more difficult to see and cut on-grain with some delicate weaves, there's another trick to ensure a straight cut:
  • Snip through the selvage, and then select a single thread, and pull it out. Once it's been removed, you'll have a clear and visible line, that's perfectly on-grain, that you can follow with your scissors.
When you can't tear, just keep in mind all of the information above above regarding how to find the grain and align your pattern to use the grain to your advantage. Ensure that your fabric is on-grain, pin carefully, and scissor away! 

Additional tips:
  •  Use cutting boards, rotary cutting mats, and pressing surfaces that have horizontal, vertical, and diagonal lines clearly marked. Depending on the materials that these are made of (ex: those cardboard mats, gridded ironing board covers, etc), some surfaces may become warped with time, and should be replaced whenever necessary.
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