Understanding Thread Counts
All woven fabrics are made up of the warp - the threads that are stretched out lengthways on the loom - and the weft,
the threads that are interwoven with the warp at right angles to it.
If we look at a conventional tartan, such as this 18th century one called Fraser of Boblainy, we notice that the pattern is the same in both directions. This is a characteristic of the great majority of tartans but we can simplify our explanation if we separate the warp from the weft like this:
These are the threads stretched out in front of the weaver and we can see more easily how the pattern repeats itself.
This pattern or sett can be written down in terms of the numbers and colours of threads included. If we start from the blue line on the left we would write 4 blue, 56 red, 28 green, 28 blue, 4 red, 28 blue, 28 green and so on.
You might notice that when we get to the 4 red, the pattern flips over and repeats itself backwards - 28 blue 28 green, 56 red, 4 blue and we're back to whe
re we started. That's what we call 
the sett - the complete pattern. The 4 red is called a pivot point and in this simple tartan there is another pivot point - 4 blue. Whichever pivot you take, you can see how the pattern mirrors itself about that pivot. If you regard the sett as an individual wall tile, then the whole tartan is the equivalent of you tiling your kitchen wall with tartan tiles - now there's an interesting commercial opportunity for someone!
This system of counting the threads enables us to record the pattern of a tartan in a very simple fashion. We choose one of the pivot points and record the threads until we reach the second pivot point: 4 blue, 56 red, 28 green, 28 blue, 4 red. That's what's known as a half sett with full count at the pivots. Designers and weavers would shorten the count and write it like this B/4 R56 G28 B28 R/4. The oblique stroke in B/4 and R/4 indicates that point is a pivot. If we had chosen the red as the pivot the count would have read R/4 B28 G28 R56 B/4 which you will notice gives you the same pattern as if you had used the blue!
Now let's have a look at the weft - the pattern formed by the flying shuttles (in traditional looms) interweaving their yarn with the warp threads. In this case we have three shuttles, one for each colour. Starting with the red shuttle, it would travel fromleft to right and back again weaving two red threads into the sett. To produce our thread count of 4 red it would do that twice. Then the blue shuttle would fly out and back 14 times (14 x 2 = 28 blue threads), then the green shuttle would make 14 journeys and then back to the red which, this time would make 28 journeys (28 x 2 = 56 red).
We ought to mention some of the little vagaries that appear in thread counts. There are three colours where, if we used their initial letters as we've done above with red, blue and green, we'd cause great confusion and the weavers would end up with some strange results.
Those three colours are Black, Brown and Grey but we've already allocated those initial letters to other colurs (Blue and Green) so each has a code that avoids that problem: Black becomes 'K'; Brown becomes 'T' for tan and Grey becomes 'N' for neutral.
One further simple way of denoting colours a little more accurately is the use of 'L' for light and 'D' for dark in front of the standard letter for each colour. 'G' on its own means that it's the medium shade. 'LG' denotes light green and 'DG' denotes dark green.
There is no standard colour palette in the tartan industry which does cause a lot of head-scratching at times when designers come up with fancy names for colours and we have to try and guess what part of the spectrum accommodates Mediterranean Mist, Autumnal Green or Spring Breeze! The use of technical colour formals such as RGB usually solves the problem but we won't go into those uncharted areas at this stage.
