This is an example of a carpet from the Museum's collection. It dates to the second half of the 16th century.
Simply looking at the design enables me to identify the type of knot used in it with a fair degree of confidence.
Look at these birds, here. Look how beautifully the head curves and the back. And then look at the leg, the separate toes - very natural looking design. This enables me to say with confidence that the knot used in this carpet is probably an asymmetrical knot.
If you look at books on carpets published about twenty years ago, you may find the asymmetrical knot called a Persian knot. The problem with calling it that is the implication that Persian knots are only used in Persian carpets and that isn't true. A Persian knot like this can be found in some Turkish carpets. Some carpets from Central Asia, Persian carpets of course and carpets from India. Asymmetrical is a much better term for it.
It's called asymmetrical because the thread used in the knot completely encircles one warp thread but only goes behind the second one. It's a very fine knot because of this. Because it only encircles one warp thread and it's possible to fit many of them into a given area. As a consequence, designs knotted with a Persian asymmetrical knot are very fine. You can get fine lines like the black outline here, beautiful curving lines and detail as well - the speckling on the bird's breast. So when you see a natural looking design of flowers, birds or even human beings, knotted in pile on a carpet the chances are it was knotted with an asymmetrical knot.