How to Accurately Mark Dark Fabric with Soap

I was so happy when I discovered using Crayola Ultra-Clean Fine Line Washable Markers to mark fabric. They work so much better than the fabric markers and pencils available at fabric stores. These markers changed my life. Seriously, they did. But of course, they don’t show up on dark colored fabric.

The main challenge I’ve had with marking on dark fabric is finding a tool that I can use to smoothly and quickly trace around a pattern onto dark colored knit fabric without stretching or snagging on the fabric. I finally realized the solution is to use soap slivers, probably something my great grandmother used to mark fabric! I can’t believe I’ve been ignoring such an obvious solution for so many years. I thought soap would make an imprecise tool at best, but I’ve discovered that I can get a nice crisp line by marking against the edge of a piece of paper.

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I had read a tip about marking fabric with soap slivers many years ago. I got out a little bar of hard hotel soap, tried using it to mark fabric, said, “Yep, it leaves a mark on dark fabric,” put it in my drawer of marking tools, and never got it back out. The reason I never used it is I thought it made wide, fuzzy marks that wouldn’t be of much use. But, as I’ve discovered, there are ways to use soap to get a nice sharp line!

There are two tricks to getting precise marks with soap. First, you need a piece of soap the right shape. If you use regular bar soap, the thin soap sliver you are left with when the bar is almost used up is a pretty good shape. The soap sliver should be about 5mm (3/16″) thick. Let it dry completely before using it to mark fabric.

If you don’t use bar soap, and don’t want to use someone else’s old soap sliver, you can use a small saw to cut a piece of hard bar soap to about the size and shape of a piece of tailor’s chalk. You want your piece of soap to be about 5mm (3/16″) thick.

Not all types of bar soap will leave good marks on fabric. The little bars of hard soap you get at hotels work well for marking fabric. If you don’t have one of those, I recommend using hard bar soap such as Kirk’s Castile Bar Soap* or Dr. Bronner’s Castile Bar Soap*. Dr. Bronner’s bar soap has a better shape for cutting into slices. If you are going to cut a bar of soap, start with a fresh, unused bar so it crumbles less.

To cut this round hotel soap, I cut off one side to give me a flat surface, then sawed the bar in half to make a thinner piece.

You can sharpen and bevel the edges of your soap sliver by rubbing the soap on fine sandpaper. Use an old toothbrush to brush the soap residue off of the sandpaper, and you can keep re-using the same piece of sandpaper.

I tried cutting soap with a serrated knife, and it mostly just crumbled, but I got some small usable pieces. So if you don’t have a saw, you can try cutting or shaving soap with a knife. If you are starting with a small bar of hotel soap, you could also try using a cheese grater or razor knife to make the bar thinner or bevel one side to get a sharp edge. You can sand the soap pieces with sandpaper to shape them further.

The second trick to getting a good line with a soap sliver is to use it up against a piece of paper. That way your line can be any width, but you know to use the nice sharp edge of the line that was against the paper as your guide. If you like you can make some stray marks on the fuzzy side of the line to remind you which is the correct edge of the line to reference.

If you are tracing around a pattern, it’s easy to remember which is the correct side of the line to reference, since you will be cutting off the soap marks. However, for marks on the interior of your pattern, you need to keep track of which side of the line was against the paper.

In the picture below, the line on the left was drawn freehand, and the other two were drawn against a piece of paper. On the line on the right, I drew some stray marks to remind me that the other side of the line is where the actual reference line is. So, with these thicker soap lines, the center of the line isn’t what you look at, it’s one edge of the line that matters.

I found that marking against paper about the weight of regular printer paper works best, but you can also trace around a tissue paper pattern if you are careful.

Marking against a ruler doesn’t work, since the blunt edge of the soap can’t get up against the ruler. When you use paper, the soap rides over the edge of the paper, giving you a nice sharp line on your fabric.

I usually go over my line a couple of times to make sure I have a good visible line, but this goes quickly since the soap glides so smoothly over the fabric.

To mark a dart, I find the easiest way is to cut along one leg of the dart on the pattern and fold it open. Trace along the edges of the dart legs with soap, and remember that the outside edges of the soap marks are the actual stitching line. Even if your soap line is a quarter inch wide, you still have a perfectly accurate stitching line, because the edge of the line that was against the paper is your stitching line.

If you are cutting your fabric on the fold or double layered, mark the ends of the dart legs and the dart apex with pins or tailor’s tacks, then flip the fabric over and mark the other side, using the pattern as a guide.

For comparison, here are the other marking tools I tried previously to mark dark fabric. None of them work as well as soap!

I tried putting cornstarch in a sock to make a DIY pounce pad, and while that worked, it was really messy and the powder ended up spreading everywhere, so I’d rather not try that again.

White Clover Chaco Liners* are great marking tools, but they have some limitations. I use them frequently to mark dart lines and such on dark fabric, but they are easier to use to mark straight lines than to trace around curved pattern pieces. The chalk lines brush away easily, but if you rub your finger along the chalk line right after you draw it, it helps rub the loose chalk into the fabric so it won’t brush off as easily. While I can use Chaco liners to trace around a pattern onto fabric, I have to work slowly to avoid stretching out knit fabric. I usually have to go over the same area multiple times while carefully holding down the fabric to keep it from stretching, and even then the marks are not always as visible as I would like.

I tried regular clay tailor’s chalk, which works a little better than a Chaco Liner for tracing around a curved pattern onto knit fabric. It doesn’t glide smoothly, so I still have to work slowly to avoid stretching out the fabric, but the marks are more visible than the Chaco Liner marks, which is good. The main problem I have with chalk, though, is I really don’t like touching chalk. The feel of the dust on my fingers brings me back to third grade and that kid that liked to scrape his fingernails down the chalkboard . . . shudder.

I’ve been using white china markers* to mark notches on knit fabric, since I don’t like to clip into knits to mark the notches, especially when I have quarter inch seam allowances. The marks seem to wash out just fine, but I still use these grease pencils sparingly and only in the seam allowances, just in case. These marks are more visible than chalk marks, and they don’t brush away. While china markers work to trace around a pattern onto woven fabric if your pattern is on sturdy paper, I find they don’t work at all to trace a pattern onto stretchy knit fabric.

So tailor’s chalk was the best option I knew of, but I kept wishing it would glide more smoothly, and I wondered if the wax based chalk tailors use would be better. I almost ordered some, but that was when I remembered soap slivers!

All these years, and the perfect solution has been in my house the whole time. Unlike chalk, soap glides smoothly over both woven and knit fabric, it leaves nice visible lines that don’t brush away easily, and since it’s soap, I know the marks are going to wash out! Tracing around a pattern with soap is much faster and easier than anything else I’ve tried.

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