Originaly designed to incorporate air into coffee or milk to provide a thick froth it needs to be noted that to not end up with your soap base looking like a cappucino you will need to follow some simple rules.
After thouroughly mixing your powder based pigmnent with a little glycerin or alcohol place your mini mixer into your melted soap base turned OFF. Pour your pigment or dye into the melted soap base and switch the mini mixer on, move the mixer around under the surface of the base not forgetting the lower corners of your mixing jug. Once your pigment is dispersed turn the mixer off before removing it from the mixing vessel or you'll get splattered.
If you follow the rules, this will be the most inexpensive yet invaluable soap making tool you will ever buy.