This is a Javascript program for designing Celtic knots.
Initially the display is a simple weave of intersecting threads.
You can design a knot by clicking on the points where the threads intersect.
The program ensures that your knot is always properly woven (over then
under).
Your knot will look best if it has some symmetry or pattern to it
(for bonus points, use a single thread).

Click once on any intersection point to make a horizontal cut.
The threads rejoin and now run horizontally past the point.
Click again to make a vertical cut, making the threads run
vertically past the point.
Click a third time to restore the point to
its original state with the threads running diagonally through it.
If you want to draw a smaller knot, just cut around its perimeter.

This program only helps with quite basic rectangular knots.
Most importantly,
it's really not very good at drawing. For example, long curves don't
look nearly as good as hand drawn ones. You also can't do knots
that fill nonrectangular shapes such as circles.
However, you can get a pretty good idea of what a rectangular knot would
look like if drawn well.

There are three standard reference books about drawing Celtic knots.
The simplest and most recent is Iain Bain's Celtic Knotwork
(published in 1986, ISBN 0806986387).
More comprehensive, but less accessible,
is his father's book Celtic Art, the Methods of Construction by
George Bain (published in 1951, ISBN 0094618305).
The earliest standard reference is
Celtic Art in Pagan and Christian Times by J. Romilly Allen
(published in 1904, Methuen & Co.).

This copy of the program uses a 30 by 20 grid of squares. If your design
needs more space, use the large version, which has
finer threads and a 60 by 40 grid.

There are lots of relevant web sites — Google or live.com can help you
find them. It's worth visiting
Direct Imagination, who publish
a CDROM version of the wonderful Grammar of Ornament.
There's also my own collection of decorative
bars.

Written by Andrew Birrell. This program and its
source code are available free.
Use at your own risk!
