Hi I’m trying to make a texture for a room in BI, and I need to know if a texture can subtract from the texture below. In other words, You have a cloud normal as one texture and a marble texture above and the marble texture removes areas from the texture below. It doesn’t have to be cloud or wood texture though. (Sorry if confusing I’m not good with words) 
You can use a texture as a stencil (see attached demo .blend file). Explain with examples exactly what you want to do.
StencilThe active texture is used as a mask for all following textures. This is useful for semitransparent textures and “Dirt Maps”. Black sets the pixel to “untexturable”. The Stencil mode works similar to a layer mask in a 2D program. The effect of a stencil texture can not be overridden, only extended. You need an intensity map as input.
https://www.blender.org/manual/render/blender_render/textures/influence/material.html#other-controls
Attachments
mask.blend (193 KB)
Thanks A lot, I never knew about how stencilling worked! Made my life a lot easier!