How can I model indentations on a surface? I'm trying to learn blender, and for fun trying to make a model of a bottle. The bottle shape is no problem, but the bottle has a special pattern in its material that needs to be cut out from it. How can i do this? I tried many different ways but nothing worked very well. I've attached an image of bottle in Blender. The pattern I want to cut out is the photo I've used as background image.

The Blender file
The secret is to model the indentations first, then use a deformer to create the twist.


Start with a cylinder with 9 sides.  Bevel (Ctrl + B) the edges and add an edge loop top and bottom, this will be the lip of the indentation.
Select the sides that will be indented.  Use polygon inset tool (I) to make them inset and indented.  





Add a Simple Deform modifier.  Adjust the angle to meet the reference image.





Add a Subdivision Surface modifier and preview the result.  Apply the deformation modifier.
Select top and bottom edge loops.  Use the LoopTools Circle tool (this requires the LoopTools addon).  





Extrude (E) the top and bottom faces and model the rest of the bottle.