Blue copper sulfate stain

[Jettowski]

I made a huge mistake and cleaned white shell stone with copper sulfate crystals mixed with water to eliminate mold growth. The end result was that it stained the shell stone blue! I should have known to try a small area first, but no. I have tried 30% vinegar, 100% acetone, muriatic acid, and baking soda. I have pressure washed. Nothing.  I am going to try oxalic acid and lastly hydrochloric acid. My very last choice will be to use a power sander. 

I was wondering if anyone knows of a chemical agent that will counteract/remove the blue copper sulfate staining in porous stone. 

Thank you

[Jettowski]

I found the answer at U.S. General Services Administration website. I used a poultice made of 1-part liquid ammonia, 1-part ammonia chloride powder, 4 parts diatomaceous earth, covered with trash bags, left for 24-hours, and blue is gone. Some places required two applications. Much cheaper than some commercial products on the market.

[Jettowski]

I mopped the stone with copper sulfate crystals and water, then went back to rinse off with a water hose. The blue didn’t rinse off. The stain was immediate.