Sometimes it means hydrochloric acid to clean brass I end up with this pattern only brass colored why is this, and is there a name for this?

There is an explanation of the etching process and the effect on the metal surface in section 9.2.2. of this document by Sharmila Mukhopadhyay:

http://www.spectroscopynow.com/userfile ... 77-412.pdf

Consider a crucible of molten brass or bronze. When the liquid starts to cool it will return to a solid state. This freezing starts at nucleation points and as the molten metal solidifies it creates a crystalline structure. The orientation of the crystalline structure or, in metallurgical parlance, the lattice, isn’t necessarily oriented with other lattices which are also freezing from other nucleation points. What you are seeing is the varied orientation of separate lattices as they grow together during freezing. These are the crystals of metal that make up the whole. This detail can be seen in many places. Brass door hardware on public buildings that are touched each day by hundreds of people will etch into this display. The navy used to have brass cannons which were polished regularly. During firing the surface would change dramatically suddenly. This meant the crystalline structure was failing and it was time to not load another round. If you work harden a piece of brass or bronze the crystalline structure is being broken up into smaller grains and the hardness is a function of increased surface area or grain boundaries. Upon annealing the grains regrow into larger grains and release the internal stresses, softening the material. Metallurgy and physical chemistry are fascinating subjects that are worth exploring. If you are adventurous look into solid state physics also.