Junior year of high school, my chemistry class learned about chromatography and related methods, then spent a day out-of-doors “tie-dying” things as a treat. The method, as I recall, was to scribble all over a piece of cloth with permanent markers, then hang it over a tub of rubbing alcohol with one end submerged. Capillary action caused the alcohol to rise through the cloth, carrying some of the dye with it, smearing out the colors. It looked, as I recall, pretty daft, although you can do beautiful things with better markers and coffee-filter-paper with this method. At any rate, I had a “tie-dyed” piece of fabric and didn’t know what to do with it. At the same time I had some pairs of jeans that my mom had bought me that tapered to the ankle and made my already-broad hips look fat, and some notion that if I flared or bell-bottomed the leg this dire situation would improve. So I cut some triangles out of the tie-dyed fabric, slit the leg of a pair of jeans below the knee, inserted the triangles, wore them to school the next day, and got a lot of comments along the lines of “oh seesawyer you are so weird”. C’est la high school. Undaunted, I did the same thing to several more pairs of jeans, with less daft-looking insert fabrics leading to better results, and ended up liking them well enough that in the following decade of wearing jeans every day, I have owned precisely one pair of jeans that I did not flare. Now I get comments like “I love your jeans!” and even a couple commission requests—and you can too!
You will need: a pair of jeans that fit well above the knee and a quarter-flat piece of cotton. If you are buying fabric by the yard instead of quarter flats, you will need a full foot (1/3 yd). The color/pattern is up to you; I like doing brown/red/orange patterns in light blue jeans, and matching patterns in dark blue or black jeans. Pictures: various jeans with brown/red panels, various jeans with matching-ish panels.
- Put on the jeans. On the outside leg seams, mark the knee just below where it bends, at the same height on both sides.
- With a seam-ripper, or if you are badass a pin and pair of sharp-nose scissors, rip out the ankle hems for an inch or two on either side of the outside-leg seam.
- Rip out the outside-leg seam from the bottom to the mark at the knee. A tip for making your life easier: the main seam of jeans is usually done in a machine chain stitch, which if you start from the correct end and side you can just pull out like frogging a piece of knitting; if you can’t find this magic quick-release thread, though, just rip out normally.
- Cut your fabric: with a quarter flat, fold it lengthwise into thirds (for a roughly 6″ by 22″ folded piece) and mark the folds at top and bottom. Unfold, and fold diagonally from the left-hand mark on one end to the right-hand mark on the other end. Cut along the fold.
- Stack the two pieces of fabric, and fold from the square corner of the long end to 1/2″ from the obtuse corner of the short end, along the short end (see diagram). Cut along the fold. You should now have two (nearly) isosceles triangles that are 22″ or so tall and 12″ or so at the base (and 1/2″ at the top…yes this makes it a trapezoid, technically), and two right triangles that are 5.5″ by 22″ which you can discard (or save for scrap quilts, stuffing, etc).
- Center the top of the triangle 1/2″ above the knee mark of a leg of the jeans and pin; pin each side of the triangle to each side of the ripped-out seam, matching edges and working down to the hemline. If you have long legs, you may need to shift this down a bit and close the outside-leg seam from the knee mark down to where the triangle ends; if you have short legs, you will just need to trim off the bottom of the triangle.
- Sew each side of the triangle to the jeans, following the original seam line on the jeans. To prevent fraying, sew again somewhere in the seam allowance with a zig-zag (machine) or blanket (hand) stitch, or whatever your favorite seam-binding method is (or just resign yourself to loose threads ticking your calves for a few weeks).
- Re-hem the jeans, following the original folds/hem line in the denim and matching it in the cotton panel. If you want this to match, you can buy gold-colored jeans thread at a lot of stores, or rip out and re-do the hem all the way around. In my experience nobody looks at the hemline of pants enough to tell.
- Repeat on the other side, and you are done!
Note 1: If you are using 45″ or wider fabric, just cut out the shape described above–an isosceles almost-triangle/trapezoid, measuring 22″ high, 12″ at the base, and 1/2″ at the top. If you have a 12″x45″, you can do this by folding in half once each way, then cutting along the diagonal from close to the fold-fold corner (1/4″ away on the short side) to the free-edge corner, then separating the two pieces at the top.
Note 2: In my opinion this looks best on jeans that are somewhat fitted to the knee—loose-fit jeans will look a little silly with this random flap of fabric hanging out. If your parents keep buying you loose-fit jeans and you want to do this, though, take heart! You can fit the jeans yourself. If the outside seam is top-stitched—if there is a visible line of stitches on the outside of the jeans along the seam line, attaching the seam allowance to the top fabric—between the hip and the knee, rip this top-stitching out before you start. Put the jeans on inside-out, fastening the fly etc so they sit properly. Grab the outside-leg seam at the knee and pull it away from the leg, pinch the fabric together, and pin close to the leg, with the pointy end of the pin pointing up. Continue pulling out and pinning in this way every couple inches up towards the hip; if the jeans fit at the hip the amount of fabric in this pulled-out flap should taper to a point close to the hip; if they don’t fit, get jeans that do. Take the jeans off, being careful to not stick yourself with pins. Sew along the pin line you have made, reinforcing at the knee and crossing the original seam line at or below the hip. Rip out the hem for an inch to either side of the seam, as before. Trim the seam to a 3/8″ or so allowance from the hip to the knee and continue cutting downwards, now angling outwards towards the original seam allowance at the hemline. Rip out any remaining seam at the bottom edge, and proceed to insert the flare panel as above.
Note 3: I’ve done this with skinny/tapered jeans, regular jeans, boot-cut jeans, and even jeans that were already flare- or bell-bottom-cut. I can’t even tell the difference between jeans that started out regular and those that started out boot-cut, so the fit of the calf part does not really matter.