If you look at all the diamond-shaped blocks you'll see a line in the center of each where the double decrease was worked. I was hoping to keep that line in the triangles to make it consistent, but it wasn't working out. I did some research online and found that others weren't totally happy with their attempts either. Next, I thought I'd make the triangle with no center line at all, working the decreases on the edges.
This triangle is on the right-hand side of my afghan and, as you can see, it doesn't look very nice. While the outer edge is straight, the block is more of a U-shape rather than a V. I scrapped that idea.
It became clear to me that I was going to have to maintain the center double decrease. I thought about the fact that the decrease line on the diamonds was going to be vertical, but the decrease lines on the right and left side edges were going to be horizontal. The more I thought about it, the more I realized that I was really okay with it.
In fact, I more than okay with it, I actually liked the fact that all the decrease lines in all the triangles would be pointing towards the edge of the afghan. I was also very happy with the sharp V-shaped edges.
As for the triangles at the top and bottom, there was no problem at all. They are vertical, like the rest of the blocks, and, they also point towards to outer edge of the afghan. Now I have 10 triangles worked on one of sides (so far) and I have a nice straight edge to my afghan. I couldn't be more pleased.
Here's what I ended up doing, and will be doing for a gazillion, more or less, more triangles!
First of all, my blocks were worked on 31 stitches, so if you're going to follow what I did, you'll have to adjust your number if you didn't use 31 as your base. Secondly, you have to use a number that is divisible by 4, plus one 1 more stitch. I decided to go with 28 +1 stitch. Working with 29 stitches instead of 31 is close enough.
Abbreviations: st-stitch; sl-slip; k-knit; k2tog-knit 2 together; psso-pass slipped stitch over; tbl-through the back of the loop. k3tog-knit 3 together.
With the right side facing I picked up 15 stitches along each side of the diamond, to give me 30 sts.
Next row: Sl 1 purlwise, k13, k2tog, k13, k1 through the back of the loop. (29 sts.)
You can just k1 at the end if you prefer but I like the snug stitch it gives at the end of the row when you knit through the back of the loop. The k2tog in the middle tightens up the center stitch and makes the point sharper.
Row 1 (right side): Sl 1 purlwise, (sl 1 knitwise, k1, psso), k10, (sl 1, k2tog, psso), k10, k2tog, k1 tbl. (25 sts.)
Row 2 and all wrong side row to end of Row 12: Sl 1 purlwise, knit to the last st, k1 tbl.
Row 3: Sl 1 purlwise, (sl 1 knitwise, k1, psso), k8, (sl 1, k2tog, psso), k8, k2tog, k1 tbl. (21 sts.)
Row 5: Sl 1 purlwise, (sl 1 knitwise, k1, psso), k6, (sl 1, k2tog, psso), k6, k2tog, k1 tbl. (17 sts.)
Row 7: Sl 1 purlwise, (sl 1 knitwise, k1, psso), k4, (sl 1, k2tog, psso), k4, k2tog, k1 tbl. (13 sts.)
Row 9: Sl 1 purlwise, (sl 1 knitwise, k1, psso), k2, (sl 1, k2tog, psso), k2, k2tog, k1 tbl. (9 sts.)
Row 11: Sl 1 purlwise, (sl 1 knitwise, k1, psso), (sl 1, k2tog, psso), k2tog, k1 tbl. (5 sts.)
Row 13: Sl 1 purlwise, (sl 1, k2tog, psso), k1 tbl. (3 sts.)
Row 14 (wrong side): K3tog. Fasten off.
You're welcome to use this technique. You can even post it on your blog or on Ravelry if you like, but with one catch. You must include a link to my blog when you do: http://www.rhythmoftheneedles.net/