What's on My Coffee Cup?

My guess is that it is a metal.

Have you tried erasing it with a pencil eraser?

I'll give it a try.

My WAG is that this mark is actually in the ceramic and has always been there since firing. This is a defect in the clay. Now there use to be a white, high gloss paint that covered this defect and you did not notice the camoflage work when you bought it. These marks appeared once the paint was removed.

It's been 25 years but I have a clear memory of being confident that there was a transfer of material. I'll try to use whatever chemical I might have to remove some of it. If I remove some and have a clean, shiny white area where cleaned then a transfer would seem to be confirmed. If dark then rubbing off white would be a strong possibility.

You've surely heard tales of people finding images on a piece of toast, etc etc. e-bay the thing and you could get a hundred more to experiment with .

What stuff/methods have you tried ?

I wish it was an interesting image. It is much harder to explain why I am interested in something that doesn't look like a religious symbol, hot babe or cute little bunny.

I haven't tried removal or reapply. Over the years the school of hard knocks has trained me that nothing that goes on like a pencil will stick like this on such a smooth surface. I shouldn't care about it since I'm not in an industry and don't have a hobby where I really need the answer. Whenever I have to use a Sharpie to make a less than permanent mark on something smooth I kick myself for not being able to remember what made this mark.

If the cup was in contact with a newspaper ( wrapped in it ) ant the temperature was elevated ( as on the dash of a vehicle ) the ink from the paper could fuse into the glaze. It then becomes a permanent addition. The ink is more mobile than the paper fibers, so the ink would transfer before the Glaze would stick to the paper itself.

Good idea but I don't know if the floor of the back seat would get hot enough.

It looks like an epoxy paint that has been rubbed into the surface with some force....

...of course plastic can be hard to remove....it might have been rubbing on some hard plastic....

My memory is that it was a solid sheet or plate but it could have been epoxy painted.

The marks seem to chatter a little rather than being continuous and smooth. If the seat was pressing against the material and the movement was a series of bind and slip motions then I guess the pressure at the point of contact could be pretty high.

This might be about as close as I am going to get.

"Porous but shiny and smooth" seems to fit. It seems a little odd since it looks smooth but if this is a common defect then all the other pieces of the puzzle seem to fit.

Ethyl alcohol doe not have any effect on the marks.

Acetone does not have any effect on the marks.

I spent about 3 minutes with a razor knife trying to scrape some of the mark off. To my unaided eye I removed nothing. I also didn't seem to add any marks or deposits to the glaze.

I don't have access to a microscope now. I might have one available to me in a week or two.

Microscopic pores seems odd to someone like me that knows nothing about ceramics but warm (hot car in Florida) plastic (or epoxy or other coating) rammed into microscopic pores in the glaze does seem to be a 100% good fit to everything I have observed. It would also explain why this same material isn't available (won't work) as a common marker for ceramic, glass and metal.

Thanks for the suggestion. Now if I just knew which storage box holds my microscope ....

You might try adding some marks with metal softer than what is used for razors. Razors are typically very hard. A fork from silverware should be a decent test; see it you can notice faint marks when you rub it with some force in the general area of the marks. The marks may be much lighter and probably a slightly different color, but should be pretty hard to remove.

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Look closely. If you can't make marks with something like a typical fork, it doesn't bode well for the porous glaze explanation. If you can then I think you are right that it is just a matter of what happened to be ramming against it in the car ride.

Take a little Barkeeper's Friend on a damp sponge and I bet it comes right off.

Thanks but having the mark on the cup doesn't bother me. Not knowing how to make marks this permanent is what bothers me. A Sharpie or paint would have come off years ago. This won't rub off, wear off, scrape off or fade. It is resistant to chemicals. As near as I can tell it is a sample of the material "unobtainium" that management typically expects to be incorporated into their new design.

Mmm, maybe KrisDel(R) or LynDoor(R) would like to buy it, reverse engineer it and sell bulk unobtainium on their web stores.

just looks like a positive lead test, I wouldn't worry

It does look like that. I think I'm OK since every night at 10 PM the classic rock station gets the lead out.

I've seen that happen to cups that are stored such that they rub together. Might be the glazes rubbed together and formed the mark. Just a guess.

That is close but it was the only ceramic item in the box. I remember when it happened but since it was on office clean out day I had more important things on my mind than a coffee cup. The cup went into a storage box and I do remember the back of the seat pushing something against the cup but I don't remember what.

Basically you are right except it was not another ceramic item. I think that your suggestion and the microscopic pores suggestion from above are both on the right track. And with the microscopic pores on a shiny surface suggestion the marks could have been made by many types of plastic or paint.

I was bothered by what seemed like a magical answer in the plastic. It seems like my target was off and the "magic" is the microscopic pores in the ceramic. That would explain what I was not understanding.

Put the cup in a microwave oven. If it gets too hot to touch after a minute, it is likely a metal as has been suggested. Many cheap ceramics can have unwanted metals and some can be toxic. Lead, Barium, and cadmium have been found in some ceramics. Although most ceramics in North America do not use toxic metals in manufacturing dishes or cookware, Imported dishes may still have them. It is possible the metal has migrated to the surface after you purchased it. Yes it should be fully ingrained in the surface and not easy to rid or impossible. I suggested a microwave test because it is easy. Good ceramic will not get too hot, metals are better conductors and will make the surface very hot after placed in a microwave oven. If I am correct, just throw out the cup. My best guess.

Cooties

Isn't the color a little too dark?

Do you think it's just a coincidence that the colour (US color) is the same as that of the printing?

It might not show in the picture but the printing is brown and the marks are dark gray. I also have a spot with dark gray marks on top of the brown printing. This pretty well eliminates the "scrape off" ideas but pores in the final glaze seems very reasonable even if impossible for me to see.

I believe you are correct. That's how it works, but it simply fills into the voids of cracks and pits.

It's paint or ink from whatever it was rubbing against.

Barkeeper's Friend and a little elbow grease will probably clean it up.

I never would have guessed that but I now think that there is a very good chance that microscopic cracks or microscopic pores (or both) are the answer.

I basically asked the question because it seemed like I was barking up the wrong tree but I couldn't find another tree to bark at. You and several other responders helped me understand it.

Thanks to all,

Bruce

But the fact that the cup is riddled with microcracks in the glaze also means that if there ARE toxic metals in the ceramic, then your coffee may be leaching them out and slowly poisoning you too....

I'm not a coffee drinker. The cup has rotated back and forth between soft drink duty and a desk top holder for resistors, capacitors, ICs, etc (yes, I know it is not ESD safe). I'll retire the cup from Pepsi duty and it will be able to devote full time to pencils, paper clips, resistors, etc.

Well, the lead in the solder on the leads of the components probably isn't helping in that regard either....=b

I can't believe y'all can't see it. . .

-A-

Try a site like the Marble Institute of America…Removing stains--I know that marble is porous, but they list the chemicals and treatments for various stains, whether organic, metal, ink, oils, etc…You will get an idea of what material removes what type of stain--Look at the poultices, that use talc, and acetone etc, covered and left for a period of time, that draw the offending stains out. We have used them successfully for many countertop stains, that cannot be removed in any other way. Worth a shot, maybe...

Thank you,

Bruce

I believe you have discovered the dark matter that makes up so much of the universe, but has not yet, (until now!) been spotted.

Turn that over to NASA and see if you get a reward!

I think this is close and about as close as I am going to get.

I have a memory of it happening but at the time it was just a small thing that went wrong on an overall bad day. Before asking this question I had assumed all shiny glazed ceramic surfaces were smooth. Once I found out that some are porous then that was the magical part I was looking for.

It was not a mouse pad. It might have been a structural foam Multibus I card cage but we only had light gray cages and this was darker. I remember it being some sort of a flat plastic or rubber sheet/plate that I was taking with me but I don't remember what it was.

Could it have been the metal bar that forms the framework for the car seat?

No, this was mid car seat. The back of the seat moved something in a rocking motion. The pile of things on top of the coffee cup and plastic/rubber sheet was applying pressure.

What had bothered me over the years was that I thought I had accidentally discovered a neat and very permanent way to mark on a ceramic surface. Once it became likely that a defective ceramic glaze was a key component then the dark mark was just another stain.

Schmutz.

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I notice in the photo that there appears to be a border around the letter C, where the marks stop and continue inside the letter? as if the lettering on the cup are stencils? this suggests extra thickness stopped the mark occurring? So if the cup had been painted white and then stenciled with the lettering, this may mean that the marks you can see maybe the original pottery, tapping the cup may spread a soft paint to expose it. Just a thought.

Regards JD.

Bruce wanted some ideas on how to replicate the observed very permanent marking on glazed ceramic surface process if and when required.

I have a souvenir cup that was post glaze printed with a photo and it's very permanent. I kinda recall there was a moderate heating step in the process. Maybe a clue there.

this was amazing.

Permanent marker, once the cap has come adrift ?