Below my green triangle I made a blue one. I started in the straight corner and made 7 rounds. In the straight corner I decreased every other row and in the other corners every row. My triangle is 3/8 inch high!
I also tried a spiral trellis on a base of chain stitches. I started to decrease in the third round. When it was finished I made one round on the loops of the chain stitches on the outside of it, 2 in every loop. I think it looks like a hat.
My last example is made on a base of 5 chain stitches. I started in the second chain stitch and worked around it. In the first round I increased 5 stitches on both ends, in the second round 2 stitches and the third 3 stitches.
So far I only used cotton perlé for my examples. The tutorials of Mary Corbet and Jeanne where a great help for me!