Crochet stitch variations may be worked in many different ways to produce many different effects. Such variations include working several stitches in the same place,working several stitches together and working in the reverse direction.
Increasing- Working several stitches in the same place is the technique used to increase the total number of stitches when shaping a garment or other item. Increases can be worked at the edges of flat pieces or at any point along a row or round.
Patterning- Two, three or more stitches can be worked into the same place to make a fan of stitches, often called a shell. As the total number of stitches is hereby increased it is necessary that other stitches are then worked together or skipped, in order to compensate.
In the illustration above five trebles are worked into the same foundation chain, thus forming a shell.
Crochet in front loop only
Crochet in back loop only
If the hook is inserted into the front loop only the empty back loop will show as a ridge on the other side of the work.
Likewise if the hook is inserted under the back loop only the empty front loop creates a ridge on the side of the work facing you.
NB Front loop means the loop nearest you a the top of the stitch and the back loop indicates the farther loop, whether you are working a right-side or wrong-side row.
Many other crochet stitch variations an be formed by inserting the hook one or more rows below the previous one.The insertion can also be either directly below the next stitch or one or more stitches to either the left or right. A double crochet spike is shown in the illustration below-