Loop, loop pearls, purl, pearl and picot are terms used to describe the length of thread left between stitches which when firmly set or snugged up is pushed outward away from the tatting. The loop term may have been first used for "picot." It, however, created confusion as the term "loop" was also used to indicate the thread around the hand in position to make a ring. Moreover, in the Modern Priscilla method of shuttle tatting, the instructions require the tatter to lay the thread from the shuttle across the back of the left hand in a "loop," also.

The purl term is often found in vintage patterns especially the early Mlle. Riego books. Please see (https://www.bellaonline.com/articles/art70461.asp) A possible carryover from knitting terms, the "purl" indicates leaving a short length of thread between stitches to create the familiar picot. (The purl or picot may be placed before or after a double stitch or a half stitch.) This term's meaning was made even clearer when the instructions called for the tatter to wrap the thread around a "purling pin", or picot gauge.
In 1851, an anonymous woman wrote a book called, Tatting Made Easy, in which the author described the joining of picots. Here the pearl term was used for the picot. "Lay the loop under the pearl to which it is to be joined."
Vertical use of picot gauge. Holding the gauge at a right angle to the work creates a picot of one width (the width of the gauge itself.) Here the gauge would be removed after each picot is closed.	Horizontal use of picot gauge. Holding the gauge parallel to the work creates a picot of two widths. For these picots, the gauge may be removed after the ring/chain is completed.

Here in the Girl's Own Book of Tatting, the term "pearl stitch" is used. To create the "pearl stitch", tat one double stitch, picot, one double stitch. Sample pattern.

First loop, 6 double stitches, 2 pearl stitches, 2 double stitches, 1 pearl stitch, 2 double stitches and close.

Modern notation:
Ring 7 - 2 - 4 - (used for later join) 3 close ring.

Second loop, 2 double stitches, + (join to previous ring at last picot) 2 double stitches, 2 pearl stitches, 2 double stitches, 1 pearl stitch, 2 double stitches and close ring.

Modern notation:
Ring 2 + (join to previous ring at last picot) 3 - 2 - 4 - 3 clr.


To review the use of a picot gauge:
https://www.bellaonline.com/articles/art1890.asp

A free copy to download of the Girl's Own Book of Tatting may be found here on the new links page or permanently on the Free tatting books online page:

https://www.bellaonline.com/subjects/2537.asp new links
https://www.bellaonline.com/subjects/3137.asp free books