I have been poulticing a stain on a red granite counter top using a clay poultice and a commercial degreaser. When I remove the poultice the area where the poultice was is very dark and does not seem to dry out and lighten. What causes this and how c

This is a very common problem on granite. Granite is a very porous stone, more porous than most marble. Because of its porous nature, granite has the ability to retain a great deal of moisture. The dark area in this case may simply be excessive moisture. I have seen some of these moist spots take a week or more to dry out, however there is a little trick to accelerate the drying process. The simplest way to draw out this moisture is to apply a dry poultice. Place a large quality of dry poultice, Do Not add any chemical additive or water, over the dark area overlapping about ½ inch. Allow this to remain on the dark area and remove in approx 12 hours. If the area is still dark, allow the dry poultice to sit longer. If the poultice becomes wet or damp remove it and apply a new dry poultice. If after 24 hours the dark area has not become lighter then there are several other possible causes. The degreaser you have used as your additive may have contributed to the darkening. If this is the case then use a plain poultice using only water as an additive and reapply. This should dilute the degreaser and pull any excess degreaser out. There is also the possibility that the original stain you have tried to remove was deeply imbedded and your poultice has only pulled it closer to the surface. Simply repeating your poultice several times should completely remove the stain.