Perhaps contact your local tile store and ask them for their advice.

Go to your local wlmart and get something called "ZAP" - this cleaning product works like no other. I would try a hidden test spot before doing the entire surface. If it works open a window and go to town. (very stinky product)
Best of luck!!!

Thanks! I will check out ZAP!

Glass tiles were often used in the original subway lines, and are being used today in many of the restoration projects in the subway system.

If your tiles are actually glass, you might try contacting J.Racenstein in New York for any suggestions about cleaning them...Racenstein supplies most of the major window cleaning companies in the USA.

Or, you might try contacting S.A. Bendheim, also in NY, they are the glass tile supplier for the subway restoration glass tiles.

What is 'crackle??' The reason I ask this is that upon ridding herself of children some time back, my mother attempted to single-handedly remove the atrocious metal tile facing (yes, that's right) that had obscured our ca. 1929 bathroom tiles for 40+ years (a 50's redecorating fancy that had, possibly, served to obscure some browing/leakage on our subway bathroom tiles). The excavation resulted in the original tiles sporting a sort of 'antiqued' look, wherein cracks in the original tiles were accompanied with browish stains, some of which could have been credited to bad installation (leakage behind tiles into walls and attendant browning), and most of which could have been attributed to that STUPID metal tile which did nothing but provide a vapor barrier in these moist environs, accelerating moisture containment and discoloration. The family concluded that the newly unearthed tile looked 'antiqued', and therefore cool; and that the excavation was essentially a success -- My query is this: is there something in 'subway tile' design (crackling?) that contributes to this browning, and, more importantly, could your time have been better spent not being privy to this 'tile exegesis?'

We're in a similar situation. We found subway tile underneath the tacky blue tile in our 1886 Victorian. My husband spent hours scraping off all the old adhesive. It wasn't until we installed a new white tile floor that we realized the subway tiles weren't really "white" anymore. One of our contractors recommended washing down with bleach to lighten them somewhat - but that ZAP product sounds a lot more practical. I will post back once we try it.

The "crackle" is the result of the glaze and the underlying tile contracting/expanding at different rates (during temperature change). The same effect is common on old pottery or earthenware dishes.

We have the same off white subway tile in two of our bathrooms (house built 1882, baths added 1910). To my mind, it is the grout that looks yucky, the tile itself looks good with a tiny bit of discoloration and crazing ("crazing" is the official term for the "crackle").

Are subway tiles with a matte finish more "authentic" to older homes than those with a gloss finish? I am doing a (semi)vintage kitchen in my 1934 spanish revival; I am wondering which finish to use for the backsplash with my soapstone counters.

I'm really torn as to what to do myself. Our master bath is shower only but has the original tiles. Unfortunately they didn't do a good job with their color selection in the first place so it is sort of hard to decorate that room. In the shower area is matte finish green subway tiles on the walls with white and black mosaic tiles on the shower floor accompanied by a row of black 4x4 tiles as a border between the wall tiles and floor tiles. The bullnose around the bathroom is glossy black. On the wall extending up about 4 feet is a matte mauve/pink 4x4 tiles - some of which are damaged ... almost as though someone took a scraper and scraped off the color. In the shower the green tiles sometimes have a brownish color which would make any reasonable person think we haven't cleaned the shower - but we do ... with tilex so it isn't "dirt". The historic aspect is nice (1932) but unless i can repair/refurbish the tiles I just don't see how I can keep it.

I have a 1927 home and the local tile store sold us a product called "The Good Stuff" that cleaned our tile. We thought it was off white but is actually white under all those years of grime. You scrub it on let it foam and then rinse well with water. It's amazing stuff.

When you are done cleaning your crackled tiles you will probably want to seal them. The crackle can allow stuff to get trapped in there and in a bathroom, that is usually pretty grungy. There are lots of sealers on the market; the ones most recommended seem to come from Miracle Sealants (the "511" line), but I'd check a local tile store to be sure.