Discoloration on granite surface plate

I left a stainless steel based height gauge (current affordable Asian DRO type) on my dark granite surface table for ~6 weeks. I now find that just where the stainless steel base contacted the granite, it's markedly lighter in colour. The area between the two legs of the base is the same colour as the bulk of the table, so the discoloration is confined to places in contact or very close to being in contact. (There doesn't appear to be any oil/grease treatment on the stainless steel surfaces, but would I detect any anyway?)

Do I just ignore the colour change - I can't feel any difference in surface texture, but then I've no idea how sensitive my delicate finger tips are!! (i.e. I'm not a builder with hands ravaged by cement etc.)

Cheers,

Reply to
Malcolm Stewart
Loading thread data ...

I cant find the reference (its on the web somewhere...) but Im pretty sure an average fingertip is capable of detecting a difference of much less than a thou, more like a ten thousanth IIRC, especially on a smooth surface. Until someone more knowledgable comes along and says other wise I wouldnt worry to much about it, especially if it stil feels ok. I assume the box you normally keep the comparitor in is showing any signs of deterioration? It might be as simple as the sweat from your hands causing the discolouration?

Dave

Reply to
dave sanderson

What are the lighting conditions? The granite work surfaces in our kitchen have darkened over time, with light patches where there are mats. A wipe over with the sealer we were supplied lightens the main area a little, but colour differences remain ;)

Reply to
Lester Caine

I've kept the surface plate in what used to be my photo darkroom (and there hasn't been an acetic acid smell for years!) i.e. it's the small ch radiator heated utility room with a permanently blacked out window, so no direct daylight, and only occasionally light from fluorescent tubes. 3 quadrants of the plate were covered with a thin opaque Teflon sheet and the height gauge stood in the remaining quadrant - open to dim light, dust, any domestic fumes (perfume from clothes detergents, gas boiler some distance away and well ventilated) etc. The discoloration is quite closely aligned with the shape of the feet of the gauge, and there's no hint as to where the edges of the opaque sheet lay for the 6 weeks. Definitely seems to be a feature of long term contact with stainless steel. Must take a snap with some form of grey scale in shot as an indicator - in case it does recover.

Cheers,

Reply to
Malcolm Stewart

Mine is discoloured by prussian blue ;-)

BugBear

Reply to
bugbear

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.