The Add texture node adds two TexturesTextures are used to add details to a surface. Textures can be procedural or imported raster files. together. The calculation is similar to the Add Layer mode used in Photoshop® to add the color values of two layers. Figure 1 shows how the Add texture adds a red color to a Ridged Fractal texture. The result is that the dark parts of the Ridged Fractal pattern are tinted red.
Figure 1 : An Add texture tints a Ridged Fractal texture with a red color