Here you will find pictures and description of the several types of pleating common to historical costume.
Knife pleats produce a smooth line down from the gathering point. In other words, a knife-pleated skirt doesn't "spring out" from the waistline, but rather falls straight down.
The "classic" knife pleat, shown to the right, has a 3 to 1 ratio: that is, three inches of fabric will make one inch of finished pleat. It doesn't matter how wide or narrow the pleats are; if they look like the picture to the right, the 3: 1 ratio will remain the same.
In some 16th century gowns, deeper knife pleats were used. The depth of the pleat was two pleats, three pleats or even four pleats deep. A picture of this is shown to the right. This allows more fabric to be pleated to a band or bodice, and produces a fuller skirt. It also makes for a bulkier seam.
Box pleating is used by many for skirts and petticoats which will be worn over bumrolls, and is used to pleat large sleeves to armscyes and pleat the skirts of italian renaissance gowns to the bodice. Box pleats are often wider than knife pleats, but the basic 3:1 ratio remains the same--3 inches of unpleated fabric makes one inch of pleated fabric.
Box pleats have more "spring" to them than knife pleats. Box-pleated skirts tend to puff out from the waistline slightly. They are also good for thick fabric, such as brocades, velvets and heavy wools.
If you're short fabric, you can get the effect of box pleats by pleating as shown to the right--very shallow box pleats. Naturally, you won't have the fullness that whole box pleats would give.
In some cases, where extra fullness is desired, you can do "double box pleats", also called "Stacked Box Pleats", shown to the right. This type of pleat requires five inches of fabric to create one inch of pleating. It will make the fabric spring out even more from the seam, and produce deeper pleats. It also creates more bulk at the seamline. This type of pleat is very handy for creating small neck and wrist ruffs--if one edge of a 2-inch-wide band is pleated in this fashion, the other side will produce very nice figure-eight ruffles.
"Stacked Pleats" are another variety of box pleat. Instead of the edges of the pleat meeting in the middle, they overlap eachother for the whole width of the pleat. They are similar in nature to rolled pleats, and a picture of a "stacked pleat" is shown in the picture below. It is the pleat to the right.
The two types of pleating listed above are the most commonly used by people. Below are a couple of "specialty" pleats, used to achieve particular effects.
The concept behind rolled pleats is simple, if somewhat hard to explain--take a large pinch of fabric, fold the pinch up until you're back to the fabric, and lay it flat. One person mentioned using a large serving fork for this purpose--place the fabric between the two fork tines and start twisting the fork, rolling the fabric as you go. To the right is a picture of the finished pleat. The one to the left is a rolled pleat. The one to the right has been called a "stacked pleat" (see the section on Box Pleating Above).
This type of pleat requires more fabric than box pleating or knife pleating. The minimum amound needed for one pleated inch is 5 inches of fabric. Depending on the number of rolls you make per pleat, this can go up to seven. Needless to say, this can create a very bulky seam line. Some people prefer to finish the top of the skirt before pleating it, and then sewing the pleated edge to a finished bodice.