Watched a DVD demo recently in which several techniques were applied to give a pleasant and convenient style.
Started with a model with hair below the shoulders a few inches and with some bangs in the front. Sections were made with a natural part on top connecting to the center of the nape in the back. At this time there was no part from the apex to the ears.
The hair in the nape was parted from the occipital bone to the middle of the ears with a slanting part on each side. The hair in each back section was combed straight down with the head bent to the front. The hair was cut with one finger (the middle finger) under it. The length was about an inch above the shoulder. The cut was parallel to the parting.
Bending the head to the front while cutting the back perimeter makes these cuts on the perimeter shorter than later cuts when the head is straight up and down. This allows the hair at the perimeter to curl under at the perimeter.
This would be the way to cut the triangular haircut in general. The slant of the partings is a guide to how much slant the perimeter hair line will have when the hair is cut parallel to the part.
The one finger elevation gives a slight graduation to the end of the hair at the perimeter. The result is a perimeter with slight graduation and a slightly increasing length of the perimeter from the center out.
The other technique used was point cutting across the perimeter. It was cut by pointing the ends of the shears into the hair to the desired guide. Point cutting at the perimeter generally makes the perimeter line softer.
A point here ( no pun intended) is that point cutting also tends to direct the hair away from the side with the short hair to the side with the long hair. This the law that short pushes long. All this means that if you want the perimeter to push in one direction then cut the points so the short side of the points are away from the desired direction. In this video the points were cut with the short side toward the center so the perimeter in the back would push away from the center further encouraging the already shorter strands in the center back (because of the triangular cut) to push to the longer strands nearer the sides
The next section in the back was from the top of the ear to above the occipital bone. It was made on an angle parallel to the first parting which had gone to the middle of the ear.
In this section, the hair was combed straight down and point cut to the guide from the first section. One finger elevation was used here also.
Next a horse shoe section was taken about an inch up from the previous section to the top of the ear. This horse shoe section extended to the recession area just above the parietal ridge. The head is now straight up and down.
The hair is again combed down and point cut with one finger elevation. It follows the guide in the back.
On the sides it was cut more like a round cut with a shorter perimeter going toward the front. This was done by angling the fingers up to the jaw line in the front.
The combination of these perimeter cuts was to give the longest length to the perimeter below the mastoid area. There was an increase in length of the perimeter from the center of the nape to below the mastoid area. This is the way a triangular haircut develops. In front of the mastoid area the perimeter was angled up like a round cut. The haircut has a slightly round look in front and a triangular look from behind.
When the first horse shoe parting is done, more horseshoe partings are continued above and point cut to the guide with one finger elevation.
Now a parting from crown to back of ear is made. This followed by pivotal radial sections in the back. These are pulled to 90 degrees from the round of the head in the back and they are point cut to follow the head shape. Cutting to follow the head shape makes the layers convex with them being short in the center, longer at the round of the head and then shorter again. This type will tend to emphasize the head shape and to cover imperfections in head shape.
The guide is taken from below in the section after the part of the perimeter that does not reach falls out. The last section behind the ear is directed back to keep the triangular shape in the back.
More radial sections are now taken in front of the ear and all are over directed back to behind the ear. Cut with point cutting.
The effect of all this is to have layers that have been pulled between 90 degrees and 180 degrees from the parietal ridge. The layers are intermediate in length, convex in shape, and help to give a pleasing head shape.
The bangs were put in with an increase in length from center forehead to the angle in the jaw. This accented the look of a round haircut in front.
A haircut with a combination of techniques was seen. In the back it looked like a triangular cut with increasing length toward the front. From the front it looked like a round cut with increasing length from the center forehead to the mastoid area. Layering was done between 90 degrees and 180 degrees ans the length at the perimeter was allowed to drop out.
The model had a strongly prominent forehead which was covered by the bangs. The lower part of the face was opened up to further draw attention to it and away from the prominent forehead.