How I Use My Sloper to Alter Patterns - 1 Front

A member of PatternReview asked me to explain how I use my sloper to alter patterns. I can't 100% vouch for my method, as I'm totally self taught and not an accredited expert, but it certainly works for me.

I'll start by explaining some terminology. Many sewists have drafted a moulage, which is a very basic top with side and waist darts that has absolutely no wearing ease at all. It fits like a second skin, and in fact is what I used to cover my adjusted dress form. A sloper is also a very basic top, but it has minimal wearing ease added. If you sewed it in real fabric, it would be wearable, though pretty boring. It has no style details. Some people also refer to a sloper as a block, but to my mind that is incorrect. To me, a block is a basic pattern that has some style details. For example, I drafted an armhole princess seam top, a shoulder princess seam top, and a basic shirt with collar, using my sloper as a starting point - these are my blocks. If I'm altering a shoulder princess pattern, I'll compare it to my shoulder princess block.

To begin the process of comparing a commercially published pattern to a sloper, here's what you need to have on hand:

• a clean traced copy of your sloper, front and back
• a copy of the pattern, with the stitching lines marked. Most patterns do not show the stitching line, only the cutting line, so you need to refer to the instructions to determine the seam allowances and then draw them in
• extra tissue or tracing paper
  
• a ruler. I prefer to use a 24" clear quilter's ruler.
• a curved dressmaker's ruler
  
• pencils or pens. I usually use a .5 mm drafting pencil, but for the examples below I used colored Sharpies. I prefer the drafting pencil since I can erase and it also doesn't smear, but the colors definitely show up better in the photos.
• Either removable tape or pins. My cutting mat is hard, so I use the tape, but if you have a cardboard mat, pins work better.

I selected Burda World of Fashion 1/2008 style # 125 because a/ BWOF patterns do not include seam allowances, so I could simply trace it, alter it and add seam allowances when ready to cut; and b/ the dart control is so obviously different from a sloper.

Start by analyzing the pattern's style. Try to determine where the dart control is located. In this case, it looks like the side dart is rotated into pleats that meet the yoke, while the waist dart is divided into two parallel tucks.
Here's the sloper with the yoke marked in blue. Cut the yoke away from the sloper, to compare with the pattern's yoke piece. I always start at the neck/shoulders and work my way down.
Here you see the pattern in blue compared to the sloper in red. Obviously, I need to make a narrow shoulder alteration.
The ruler tells me it's a 3/4 inch narrow shoulder adjustment.
I mark where I will slash the pattern (in green). Slashing is almost always either parallel or perpendicular to the grain, to preserve both style and grain lines.
Overlapping the pieces by 3/4 inch.
Because I made a narrow shoulder adjustment in the yoke, I need to carry it down into the front. Here I've marked (in red) a box around the armhole - one side parallel to the grain, and the other perpendicular. Apologies for the inconsistency of color - I worked on this over a few days as my neck issues permitted.
Using the ruler to overlap 3/4 inch.

Note for the next few pictures I have matched up the center front and waist of the pattern to the sloper. Remember, the center front of this pattern is NOT on piece 1, it is actually on the button placket. Something to keep in mind when altering - determine where the actual center front is located.

Assessing where the top of the pattern sits vis a vis the sloper, and also where the armhole is located (unfortunately not shown), I decide I need a petite armhole adjustment.
Drawing a line (in red) perpendicular to the grain where I will slash and overlap for the petite armhole adjustment.
Marking the sloper in preparation to rotate the side dart to the top pleats. I picked two spots each about a third in. I also marked points 1" above and 1" to each side of the bust apex. Finally, I drew a line from the top to each marked point and then angled in to the bust point.
I cut along the lines I just drew to, but not through the bust point. Tip: Reinforce the bust point with tape. I also cut through the midpoint of the side dart to, but not through, the bust point. Overlapping the black dart legs, which go all the way to the bust point, forces the top parallel darts to open.
Comparing the sloper (in red) to the pattern (in blue) at this point in the process and it's looking pretty good. I'm not sure about the top pleats - it looks like the pattern will take up less fabric than my sloper changes will indicate - but until I've gone through the whole process I'm unwilling to commit to any changes. It might be that the changes further down will change this dynamic, so I'll let them go for now. Judgment call - they do occur.
Now I'm going to tackle the parallel waist darts. On the sloper, I've slashed up to, but not through, the bust point at the waist dart. And then I overlapped the black dart legs, the ones that go all the way to the bust point but which would never be sewn that way. That forces the parallel pleats at the top to open wider.
After closing the waist dart, I drew in the parallel darts. Again, I picked two points on the waistline that seemed to approximate where the darts fall on the pattern. Then I picked out points that were 1" below and 1" to each side of the bust apex. Then I connected the dots from waist to points to bust apex.
I've slashed and spread the waistline parallel darts. Here you see the adjusted sloper over the pattern. I'm not sure what to think at this point. The pattern looks good compared to the sloper except for the top pleats/darts. I think I need to leave this issue for a muslin.
Here's the completed front piece altered. In a nutshell, I did a 3/4 inch narrow shoulder adjustment, a 3/4 inch petite armhole adjustment, and added about 1/4 inch at the sides. I'm leaving any other adjustments to a muslin.

I'm about halfway through my process - although I have to tell you, I rarely go to this level of detail any more. Once I figured out my "usual" alterations, which took about five tops going through this process, I didn't need to go to this level of detail anymore. I pretty much just do my standard alterations - narrow shoulder, petite armhole, add a bit to the side seams - and if it's a really different pattern in terms of dart control I'll sew a quick & dirty muslin.

Part 2, the Back, will be tomorrow.