19. Pattern Grading
What Is Grading? How Do We Do It?
Grading is the messy and confusing part for most so let's start with some definitions. Grading is the process of creating ever increasing/decreasing sizes of something that is primarily the same shape as the original. Typically we start with two sizes (smallest and largest) and then start the process of breaking up the space in between those two sizes into gaps. Look at the image below ... I have two pentagons; one representing my smallest pattern and one representing my largest.
Now in the far greater majority of cases we simply draw a line between each node and break it up into equal gaps then join the dots (see top left image below). That's it ... that's grading explained simply. The line is straight, or linear. The distance between each node on the line is the same, or equidistant. But keep in mind that it's not always like this. The spacing between the dots might increase with increased size (non-equidistant) and the line may also be curved instead of straight (non-linear, typical of plus size inclusion)
So we can mix both of these to get four different methods for working out the gaps between the smallest and largest sizes ...
A straight line with equal distances is easy, but how do you know what the spacing is if you go the non equidistant route. This method is about increasing the gap between sizes as you increase in size (see top right image above) ... its got very little really to do with actual sizing and more to do with how many people will fit into each RTW size. Demographically speaking there are more people that fit into the smaller sizes than the larger sizes. So if we broke up the smaller sizes into smaller grading gaps the majority could get a better fit ... at least that's the theory. The contra argument is that, while there's less of them to account for, the larger sizes with more variation in shape get less fit options. It comes from a desire to better satisfy the majority while still providing something for the minority AND being able to better control how many of each size you manufacture ... it's about business reality. The issue, though, with plus sizing as we explained before ... is not about how many plus sized people there are but that just one graded shape won't solve the fitting issues ... plus sizes need both more sizes AND more shapes
To determine how much to increase the gap between each subsequent RTW size is an arbitrary business decision and nothing to do with anything else. Generally I find people do things like gap 2 is 10% bigger than gap 1, gap 3 is 10 % bigger than gap 2, etc ... this increases the gap with each size even though the percentage is the same ... it's non-equidistant. Equidistant would be gap 2 being 10% bigger than gap 1, gap 3 being 20% bigger than gap 1, etc. They aren't the same and the distinction is very important (see image 2).
Now for the fun one; non-linear (see bottom two images above). This is something I've started seeing only in more recent times where there are a much wider selection of sizes than the usual 5 or 6 standard RTW options. It's pretty much come from the desire to satisfy an ever increasing group of plus sizes ... don't get me wrong, two paragraphs ago I said that weren't that many and there aren't demographically speaking, but the number in that group is indeed growing, especially in places like the USA and Western Europe. Previously We had normal sizes and plus sizes and each was a linear grade (dual linear) ... the plus size grading line being shallower than the normal sized line because after a certain point we decided that people got wider faster than they got taller. The argument then became at what point do we change the angle of the line ... which size is arbitrarily the start of plus sizes? So instead it stopped being a line and became a curve ... or non-linear (see images below - green represents the plus sizes). I have only ever had two clients who have gone this route because I believe others found it hard to work out .... two straight lines was easier (or 1 straight line for normal, and 1 for plus: two different grading jobs). I never liked it much until I recently started designing body forms with zero ease and found it essential to getting everything right ... at zero ease it must be a curve or your middle sizes don't fit!
All this is based on the pattern maker creating two sizes to begin with ... the smallest and the largest. This is without a doubt the most common way to grade as it removes all the complex formulas and mathematics that you need if you grade up and down from a single size. I've honestly never understood why people grade from a single size .... the argument is about time saving which is cool if you've got a fashion CAD program with all the complex math rules programmed into it. But if not then it's faster to draft two pattern sizes and grade between them than it is to work out a grading rule set.
If you've designed your patterns off a block then it's quite likely you've already bought a fully graded block set or made your own according to whatever drafting method you used ... if you can make one block to a method then you can make two, right? .... and you only ever need to make these two sizes once. So let's just assume for a second that you do have a set of graded blocks for whatever you're doing. I, for example, as a swimwear pattern maker have a fully graded set of 12% negative ease swimwear blocks (obviously I have many others but I typically use this one). I choose my largest and smallest from that set and open them in CAD. Then I draft my design twice, once onto each block, step by step ... so I end up with two different patterns ... one in the smallest size and one in the largest size. If I was doing plus sizes I'd probably add the largest plus size to the end and draft all three concurrently from scratch (much like the green section in the image above).
This is without a doubt the easiest way to grade on paper ... a simple straight line between two similar points on two pattern pieces, broken up into even gaps.
But it's even easier in CAD. In Corel draw I select my smallest size and my largest size (see image directly below) and hit the blend button (next image). It asks for how many items between the smallest and largest and I hit apply ... Corel Draw spits out all the in between sizes in one click ... linear equidistant grading at its fastest without expensive fashion CAD software ... Adobe Illustrator does a similar thing. It's instant and perfect and you don't need complex grading rules or fashion specific software.
Both Corel Draw and Adobe Illustrator blend evenly along a straight line by default, but they will also blend along a curved line (called Blend to Path in Corel) ... you just select the two sizes, the curved line representing the path (you need to select all the curved lines between nodes), tell it how many between smallest and largest and it'll spit out the new graded sizes.
But wait there's more! While Corel Draw comes standard with equidistant blending, you can edit the button's script to change from equidistant to percentage or logarithmic or any complex equation should you wish even though you'll rarely if ever use it ... it is still possible ... I created my own scripted button for this to make the process faster ... I doubt most will ever require anything like this.
But what are the gaps if I want to do it from one pattern? I used to give people an idea of how much to grade between sizes. In non-stretch people tend to use fixed arbitrary increments that show very little mathematical relationship with reality. In stretch patterns we use percentages... it only works, however, when the amount of ease is the same between sizes. If you're mathematically alert you'll immediately realize that a percentage negative ease is not an equal increment between each size. Instead it is proportional to each size. Let’s consider this for an Australian RTW size 10 bust measurements;
Size 8: 80cm x 12% reduction = 70.4cm or 4.8% smaller than size 10
Size 10: 84cm x 12% reduction = 73.9cm
Size 12: 88cm x 12% reduction = 77.4cm or 4.8% larger than size 10
Size 14: 92cm x 12% reduction = 81.0cm or 9.6% larger than size 10
So if you start with a size 10 you have a difference in bust measurement of 4.8% per size. These calculations will come out the same no matter what negative ease you use, as long as it's a percentage and not a fixed amount (like you would have learned for non-stretch). Now keep in mind that each size category is based on a standard metric bust measurement and that all the other measurements vary depending on your market demographics. True proportional grading means you'd grade by percentage across all horizontal measurements. In other words your waist and hips, for example, would be accurate for a size 10 but applying 4.8% per size would lead to minor variations in other sizes.
But what about the vertical? The length of our one piece blocks are nape to waist plus waist to crotch plus 1/2 Gusset. If we try those based on the size 10 again we get;
Size 8: 39 + 24 + 8.5 = 71.5 or 3.1% smaller than size 10
Size 10: 39.5 + 25 + 9.25 = 73.75
Size 12: 40 + 26 + 10 = 76 or 3.1% larger than size 10
Size 14: 40.5 + 27 + 10.8 = 78.3cm or 6.2% larger than size 10
So again, if we start with an Australian RTW size 10, we get a difference of 3.1% per size completely irrelevant of how much ease we apply. Of course, on paper, you still have to calculate every single point if you're grading by hand, but always by the same percentage. You never have to remember fixed incremental amounts ever again. The massive advantage, however, comes if you have a CAD package. For the incremental method your computer must know where your nodes are before you can grade and this requires specialist software which is expensive. For the proportional (percentage) method you can skip having to calculate the true increments, ignore that nodes even exist, and simply scale up your block or pattern a fixed percentage for horizontal and a fixed percentage for vertical. It's so easy it means any simple off the shelf CAD program can do it, cheaper, faster and just as accurate.
This is a good way to get your second size. You could use this way to get all your sizes but things don't always work out the best if you just apply flat percentages. For example ... your body length might increase by 3.1% per size, but your armhole height might increase only 2.6% ... hence why the fixed increments were used .... but really its a matter of knowing where things change with increased body size. So I start with my smallest size, apply a percentage to get my largest size, tweak the pattern to bring parts of the largest size back to reality, then blend between the two. In CAD this is remarkably easy, fast and incredibly accurate.
CAD will save you the time that you might fear you'll lose having to learn the software ... but it's even more important for a bigger reason ... taking less time to do a job means getting more jobs done in the same time ... or more profitability!
Lastly I have one comment that I really unfortunately need to make. NEVER GRADE A PATTERN WITH SEAM ALLOWANCE ADDED. Always add seam allowance after you've finished grading. If your pattern has seam allowance already added then remove it prior to grading. Why?
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You need to verify the seam lengths of each newly graded piece match up correctly.
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You don't want to grade the seam allowance itself (ie; seam allowance getting bigger with increasing size).
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You want to create a habit of doing things in a specific order so you don't forget steps.
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If it's unmarked and presumed by you, others who use your work later might think it hasn't been added and add it again so always clearly mark on your pattern how much seam allowance is added and where (if it's different on different parts of the pattern).
Size and Shape Envelopes
So we understand the concept of an increment between sizes ... how much should that be and why? Don't automatically think the standard 4" increment (10cm) is, well, standard for small medium and large in most countries its a bit less (8cm) ... and where you have numerical sizes (like Australia's 8 10 12 etc) it's only 4cm between sizes. These increments are designed such that you have an acceptable fit no matter where you are in the size range if you select one of the sizes .... a failure in grading is where you sit in a gap between sizes in which fit is unsuitable in the size either side. This is where we talk about fitting envelopes so let's start at the beginning .....
Size envelope is a pretty simple concept ... it's where a garment made for say an 84cm bust line will fit people anywhere from 80cm to 88cm (an 8cm size envelope). Typically we see such things in online sales shops where you might see a size Medium listed as fitting a 2" envelope or even more. The size envelope is not the convenient arbitrary thing most untrained designers and pdf pattern makers treat it as ... it's a cold hard numerical value based on the fabric weight and rebound, and the negative ease used in the pattern. When you try on a medium and its too big, but the large is too small you can tell immediately that the size envelope is less than one full size ... this is literally poor pattern making. To have an adequate size envelope, one size's envelope must overlap with the envelope of the size above and below it .... this ensures that you garments will reasonably fit anyone of any size within your total range ... no gaps.
How do we do it? Well let's take a look at the numbers. Firstly, that 84cm B cup bust measurement when reduced to 12% negative ease is 73.92cm, secondly we have determined we want to keep our negative ease within the range of 10 to 14% to avoid shear when the person moves and twists, and to stop the garment moving by itself (stability). If we run the numbers for 4cm either side of the original size we get ...
80cm in an 84cm bust is 7.6% negative ease
84cm in an 84cm bust is 12% negative ease
88cm in an 84cm bust is 16% negative ease
... which is well outside of our acceptable negative ease of 10-14%, meaning that while it might look ok and feel a bit tight or a bit loose, the fit will most certainly be compromised, shear ripples will show up much sooner and the garment will just not stay in place when you move. This is the problem with pretty much 90% of the size tables you see on the Internet ... the tables envelope is bigger than the garments practical envelope, leaving "fit" gaps between each size ... or gaps in which the fit isn't really good enough. Good designers know how to move tension around to widen that envelope ... typically they'll use less horizontal tension along the bust line and balance it with a little extra angular tension for example ... there's lots of ways to do it (and I can teach those too) which come from the experience you see in better quality brands.
Have you ever seen those people who say they were never able to find a good fit in retail ready to wear so they thought they'd do something about it and make something that better fit people? All people? And strangely enough their patterns look just like everyone else's only slightly smaller or larger! All they did was adjust that pattern to fit their own body type and regrade and think they solved the world's problems when all they really did was just move a the fit envelope along the grading path a quarter of a size or less ... the gap between sizing envelopes is still there, only now its affecting other people, and the previously affected people are all now fitting just fine. They didn't fix the problem, they moved it onto other people. Fixing the problem means having a size envelope wide enough such that there's an overlap from one envelope to the next. Pretty simple concept really but not something that's understood by many. Pretty much if you have a size table with ranges wider that 8cm you've got problems ... and that's universally all American sizes because they're 4" or 10cm ... Australia and Europe are generally only 8cm and even that is a bit much as you can see above, but at least that you can tweak for that little bit in the pattern itself if you know what you're doing ... 10cm is just not possible with your average stretch textile no matter how good you are.
Now that's size overlap. If you thought that was tricky then shape overlap will blow your mind because it compounds the issues with regards to size. Size overlap is a two dimensional concept that's been around for three decades in stretch ... I know, because I'm the person that introduced the concept to stretch pattern making 35 years ago. I thought back then it was the answer to everything because I had discovered negative ease in stretch was a percentage and not an increment ... and back then that was a big thing that took a lot of convincing people ... nowadays it's common knowledge. Shape overlap is an entirely 3D concept that views a fit envelope as a 3D contour map that explains shear ripples, tension failures and instability in a way that computers can read and then automatically adjust patterns to optimise stability and reduce shear. It's the pinnacle of understanding how stretch textiles change dynamically. Ok how do I explain how a textile behaves dynamically?
Do you remember me telling you that when you narrow a piece of fabric to the width of a strap, it over stretches? Well it also narrows further when it stretches. That's because tension will try to compensate in 3D ... if you stretch in one direction you'll narrow the perpendicular direction. If you widen the horizontal you'll shorten the vertical and vice versa ... do that in several places and that lengthening and shortening becomes cumulative and behaves in extraordinary ways. Take a look at the illustration below ... this is a very basic idea of the concept and in reality it wraps the body in 3D. Typically the waist has slightly higher negative ease to help lock things in place and minimise this distortion and help to prevent a garment moving up and down the body. So if you were to put that 80cm person into the 84cm garment like we talked about earlier you drop the negative ease in the 2D linear horizontal direction ... BUT you'd also allow the garment to lengthen over the bust vertically, dropping out all the support you previously had. This concept goes for all combinations ... and that's just for bust and hips ... we can forcefully stretch the vertical too (eg; taller people) which increases horizontal tension proportionally ... and so on and so on. 3D tension mapping is a night mare.
What this means is there's a limit to how much variation in shape a particular size can take before it becomes unstable and has all sorts of fitting issues. We adjust for these things automatically without a second thought when we make custom swimwear ... we do it everyday ... we see the ripples or the hungry but or whatever else and know how to adjust for it to make it fit correctly. Our bodies were outside the shape envelope for that standard block so we adjusted it accordingly. But in ready to wear we don't get that opportunity ... we're buying it as is off the shelf with those very same problems. Shape envelope is the amount of variation in shape a particular size can take before these problems appear ... and it's smaller than the simpler size envelope. So in real terms, that inadequate 4"/10cm difference in American sizing will have an uncomfortable gap based on size, but the appearance of fitting problems like ripples will show up well before that ... we've just come to accept that as normal. In the Aus/Eu 8cm gap there is a much smaller gap in the size envelope and the same shape envelope issues but they seem to show up at the same time and both can easily be tweaked at the pattern level. This really advocates for the US to move to the Aus/Eu sizing increment but I can't see it ever happening.
The good thing about computer modelling with tension maps is you can see the different tensions in different colours and the computer can map out the shear lines and angles on a mannequin. You may have seen a very basic and inadequate version of this in programs like Clo3D, but custom designed software for big brands and manufacturers is far more sophisticated and not only shows you exactly where your tension problems are but can show you how to fix it for the greatest stability and widest shape envelop possible ... this is precisely what I've done with the teens, adults and extended sizing blocks and the increase in shape envelope is phenomenal.
So what other things make shape envelope narrower (harder for standard ready to wear sizing) besides the increment? Firstly, too much negative ease is the biggest one ... if you can back that off it's usually going to help stability significantly, but you can't go too low or you lose stability as well. I'm really referring to those who like 15-20% negative ease ... it just doesn't work unless you have very small size increments in your sizing table. The second one we've tested (and I'm going to say I told you so) is reversible swim with two layers of top fabric .... in regular fabric this can reduce your workable envelope (depending on design) to less than half of that done traditionally ... that's right ... less than half ... meaning more than half of your buyers are going to say your sizes run small compared to what they think they should be wearing ... and that's before you vanity size!!!. But there's more to this with reversibles ... the envelope isn't just smaller, but the amount of instability increases exponentially so they are without question the most unstable swimsuit concept ever created. Don't do it unless you have no choice because you've lost half of your market before you start and doubled your potential complaints ... compared to traditional methods.
The easiest way to increase size envelope is by using lots of small narrow pieces that stretch more easily before destabilizing .. strappy things, cut outs, monokinis, and string ties. Counter intuitively, multiple seamed panels improve stability significantly over single large panels and thus increase the shape overlap. This is because you can better line up the direction of greatest stretch and therefore delay the onset of shear tension.