Did the muratic acid etch the old slate?

I have an indoor black Italian slate floor which is about 40 yrs old.  I recently added on and utilized the same slate flooring in the addition.  We removed the finish from the old slate using a paste type paint remover (Strypeze), removed the penetrating sealer with a 10% soln of muratic acid and then neutralized it.  We reapplied the finish on the old slate and it is lighter than the finished new slate(the new floor transitions into the old floor).  Is there a black stain to darken the old slate?  Did the muratic acid etch the old slate so that it can never be darkened further?

 Thanks

 Mark.