This is a new improved version of the pattern. I find it easiest to work from an abbreviated pattern so that is what I give below with an explanation of the abbreviations. I hope it is easy to understand.
My original cross.When I used #10 crochet cotton and a 1.25mm hook (Blue cross) it came out about 4 inches high and three inches wide. (10 x 7.5 cm) However using a smaller hook will give a firmer though slightly smaller bookmark. (Red cross)You could also try multi-coloured thread. For this I used a 1.25mm for the starting chain and a 1mm hook for the rest. I also increased the picot stitches from two to three.This is what I think of as the improved pattern.
Celtic Cross Bookmark
Start with at least 158 chain. Ideally make a few more to allow for missing the odd one or miss-counting. Excess chains can be undone at the end.
You need to crochet into the loop at the back of the chain. (Method 4 in my tutorial.)
The starting chain should not be too tight or you will not be able to find the loops, especially the ones after working the corners. I found using a 1.25mm hook for the starting chain and then a 1mm hook for the rest of the cross worked best but you should maybe experiment to see what works best with your crochet style. I know I work a little more firmly than some.
I find it easiest to work with an abbreviated pattern, so here are the abbreviations.
Corner = (2tr, dtr, trtr) into first ch, 3ch ss into 3rd ch from hook, (trtr, dtr, 2tr) into next ch.
V = 2tr into ch.
N eg 12 = 1tr into each of next 12 ch.
First V = tr into 3rd ch from hook.
Corner = (2dc, tr, dtr) into first ch, 2ch ss into 2nd ch from hook, (dtr, tr, 2dc) into next ch.
V = 2dc into ch.
N eg 12 = 1dc into each of next 12 ch.
First V = dc into 3rd ch from hook.
(V 4 V 1 V 1 V Corner V 1 V 1 V Corner V 1 V 1 V 4 V V 4 V) x 3
V 12 V 1 V 1 V Corner V 1 V 1 V Corner V 1 V 1 V 12 V V 4 V
Tie trefoil knots first then interweave centre and sew ends together. Join should be underneath circle when cross is complete.
Then make circle.
(V 1 1) x 8.
Interweave round centre of cross and position so join is underneath.
For a bookmark you could add a cord at the top or bottom as I describe at the bottom of these patterns – https://rainbowjunkiecorner.wordpress.com/cross-bookmark-pattern/
To use as a bookmark this definitely needs to be stiffened though I think some spray starch is enough. It is necessary to pull the corners firmly and pull the strands into exactly the right place before stiffening.