Knitting and so on: Ammonite Potholders

I always wanted to knit a spiral from within, but I didn't quite know how to go about it. I got a first idea when I thought about it waiting for my train in the morning ... something like: knit small triangles with short rows, increase one stitch per triangle and so on. Then I tried it the next time I had some time as well as the materials (yarn and needles - on a longer train journey :)
It made me quite proud to manage it in one color, but you need the right yarn to make the shape show up nicely ... and I didn't find that sort of yarn in cotton. So the obvious solution was to use a second color for contours.
These pieces can be used as potholders or coasters or as washcloths. Since they are done in intarsia, they look good from WS, too. They are knitted all in garter stitch which gives them a nice squishy texture.

This work by Knitting and so on is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

Materials

a total of about 25-30 grams cotton yarn in two colors - I used Aran weight for both (about 9 grams for C1 (blue) and 15 grams for C2 (white), but my scales are not really exact)
3.5mm knitting needles - I used short dpns
a tapestry needle to weave in ends

Techniques

Intarsia: Changing colors with the intarsia technique - as shown in this YouTube video by knitwithpat; or this YouTube video by Francoise Danoy. That way you don't have to carry long strands on the WS. The picture below shows the RS and WS of the piece.

Throughout the pattern, the following notation will be used: "C1 (k2); C2 (k3, w+t, k3); C1 (k2)" means "knit 2 sts with C1; change to C2 and knit 3 sts with C2, wrap and turn, knit another 3 sts with C2, then change back to C1 and knit 2 sts with it".
I.e. color is indicated before the knitting instructions for that yarn. the knitting instructions for that yarn are given in brackets after the color and color changes are indicated by a semicolon.
Short rows with wrap and turn (w+t) - as shown in this YouTube video by Very Pink Knits.
Joining to rows at the edges: There are various ways to connect the last stitch of one ridge to the first stitch of another. I used the following one where I joined from the RS: I knitted to the RS row, drew a loop through the edge stitch (see pictures below), then turned and did a k2tog of the the newly picked up stitch and the next stitch of WS. I will call this sequence "connect" in the pattern.
However, there are other methods to join rows at the edges, one method is shown here: http://youtu.be/3zPXZ4cu66Q . Please note that whatever you do, please stay consistent throughout the piece.

Gauge and Size
In garter stitch 4 ridges (i.e. 8 rows) gave 2 cm.
The pieces I knitted measured 18 cm in width and 16 cm in height.

Construction

The piece is started right in the middle with only a couple of stitches. During the first 7 sections, the stitch cound is increased by one stitch per section. Each of these section consists of one (complete) row in C1 and short rows in C2.
After finishing the first round of the spiral, the stitch count stays the same, but the sections consist of are full rows in C2 as well as of the short rows. The number of these full rows in C2 increases by one per section.
The last section is made up of full rows entirely.

Instructions

Setup Section - completely in C1

CO2

Row 0 (WS): kfb, k1

Ridge 1: sl1, k to end, TURN, sl1, k to end

Ridge 2: sl1, k1, w+t, k to end

Ridge 3: sl1, w+t, k to end

Section 1

Ridge 1: C1 (sl1, k to end, and pick up a stitch from the side, TURN, sl1, k to end) - on illustration 1 I have marked the point where I picked up the stitch in pink, and on illustration 2 how the piece looked afterwards. Picking up stitches from somewhere at the end of the RS row helps to close the potential hole in the middle of the piece. Alternatively, you can knit RS to the end, turn, and do a kfb into the next stitch of ridge 1. Then you have to sew the hole shut at the end. - This applies to all ridges 1 in sections 1 to 7.

Illustrations

Ridge 2: C1 (sl1, k1); C2 (k1, w+t, k1), C1 (k2)

Ridge 3: C1 (sl1, k1); C2 (w+t), C1 (k2)

Ridge 4: C1 (sl1, w+t, k1)

Section 2

Ridge 1: C1 (sl1, k to end, pick up a stitch from the side, TURN, sl1, k to end)

Ridge 2: C1 (sl1, k1); C2 (k to 1 bef end, w+t, k to 2 bef end); C1 (k2)
Ridge 3: C1 (sl1, k1); C2 (k to 1 bef last turn, w+t, k to 2 bef end); C1 (k2)