I used a lovely pink textured knit for this mermaid style dress.  I love this pattern because it is just two pieces.  Both of these dresses are made from the same pattern.  There is only a back seam and it slides onto the doll as a tube shape with no side seams or fasteners.  I did not line this dress because the fabric is fairly thick, but I loved the textured pattern.

I put a small gather at the bodice to give it more shape, and had to put a few stitches at the top of the back fishtail to control the shape.  I did not put elastic at the top of this dress.  I just sewed it tight hoping to take up some of the bulk of the material.

The belt was made from a decorative piece of trim with snaps at the back.  This dress can be a lot of fun to accessorize.  Here I have used hair scrunchies as shrugs for both dresses.  Below, I made a shrug-tube from white acrylic fur.
These are long dresses adapted from a free Tonner gown pattern by © m.dita 2009
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Just put your doll's arms straight back and push the scrunchie up to her shoulders.