Summary

You want to create a hand shaped cup?

Then you can start at once by skipping the first two steps using the generated .obj-file.

Or you can try to generate your personal thing from any 3D-Model by going through all steps of the instructions.

I designed the cups with this software:

OpenSCAD
Meshlab
Sculptris(R) Alpha 6 (Get the free alpha version)

Instructions

Here I go roughly through the building process:
Step 1: The Basic Shape
You will need a basic shape version of the cup. You can use my OpenScad script to build a basic version of the cup. Build the STL-file.

You want to skip that step? Use "basic_cup.stl" from the download.

Step 2: Optimizing the Basic Shape
Because the mesh is not optimized for a free hand mode, you will need to use meshlab. Open the stl-file in mashlab, Then choose the filter (sub menu: Remeshing, Simplification and Reconstruction) Uniform Mesh Resampling. Check the "Clean Vertices" and "Multisample" option. Set Precision to 0.5%. Then apply the filter. Now you have generated a new mesh, but the original mesh still exists on another layer. So activate the "Show Layer Dialoge"-Buttom and "delete the current mesh" by the right-click-menu after choosing the layer 0 with the original mesh. Then export the mesh using the "Alias Wavefront Object - *.obj." option.

You want to skip that step? Use "cup_4_sculptis_lowpoly.obj" from the download.

Step 3: Free Hand Modelling
Now you can import the *.obj-file into Sculptris(R) creating a new scene. Have fun! (Read the documentation how to use it in detail.) Try not to change the bottom of the cup by accident. After your work is finished export the art as ".obj"-file. You can convert the obj,-file to a .stl-file using meshlab.

You want to skip that step? Use one of my cup designs from the download.

How To Sculpt A Cup