Peter mentioned recently how to do it in a video, you have to soak it in a plastic tub and it was not just over the counter peroxide, but it would not harm the enamels but he was talking about making discolored cracks on surface less noticeable. Hopefully someone will know the exact process, good luck, if you do it then soak in water for an equal number of days after soaking in the peroxide. I think you can buy the super strength peroxide from a beautician (according to Martha Stewart years ago), but I think Peter may have recommended a hardware store. Maybe just email him. Sharon

So far I have only tried it on blue and white. I put a drop of ammonia into a 6%/20 vol. peroxide. The ammonia helps but isn’t absolutely necessary. For hairlines I drench strips cut from cosmetic cotton pads and put them on the discoloration then cover with cling film. I renew the peroxide after some hours if necessary. As Sharon said soaking in water for a day or two afterwards is important. In my opinion overglaze colors should be no problem but I would avoid gold areas. If the discoloration is on white areas only you can work with small pieces of cotton pad that you cut accordingly. 

@shinigami Sounds a safer method. Sharon

@shinigami

@sharonp

Thank you. This being a rose medallion piece there's no avoiding the gold except on the inside, and even there, there is a professional repair with gilding. 

However, as I examine it closely, the grey spots seem to be under the glaze, making me think it's just a quirky firing flaw. I may not be able to remove them at all!

You can try to clean the spotted areas on the inside by using peroxide drenched cotton pads locally. As long as you keep out of the gold there’s no problem 

@steve Might just be impurities in the clay, I would just live with it instead of messing about with the gilded areas.

I never used peroxide, because it is yellowing in time if it can’t be removed completely. A chemist friend did suggest me to neutralize the remnants of peroxide with some acid, like the lemon juice; thus I thought that all this means that something may remain, and so I think that it is better to remove than leave something in the cracks.

What I do is soaking the whole piece in ambient temperature water added with enzyme-based dish detergent (basically, all modern dish detergent contains enzymes) for a day or night. Then inspect it, and if necessary, let it soaked a further day in the same bath.

After this, in some cases the treatment will not have effect, but in most cases the staining of the crack will appear more faded. At that point, I rinse the piece with fresh water and clean the crack with a water pik, a family dental water jet. The pressure of the jet will remove the softened stain, and in 90% of cases the crack or hairline will be completely cleaned, the staining full removed.

Before doing this method, be aware that the unglazed areas, i.e. the foot, will turn pure white. That means that the very pale brownish color that we think is the normal color of the paste is indeed dirty. Thus, the pure white foot will look as it was when brand new. Many will not like that. If you want to preserve the current aspect of the foot, then the soaking of the foot must be avoided.    

In my experience, all type of enamels are very stable. I have used paint stripper, a very strong agent, several times and never had problems, including on gilded areas.

I think that what happened inside your pitcher is staining under the glaze, having the staining substance penetrated the glaze through burst bubbles holes. This is almost impossible to remove, because, due to the almost perfect impermeability of the porcelain, it took many years for staining it, hence the same is expected for the penetration of the cleaning agents.

Regards,

Giovanni

@clayandbrush

Dear Giovanni,

This is very helpful information. Thank you!

I agree that the spots on the white part will be impossible to remove. They're not just inside but outside too in many parts. 

I will keep your advice in mind if I ever have to clean an item in the future. 

Regards,

Steve

@shinigami

That's a good suggestion. I'll look into the cost of trying that, but as I look at the grey spots under a magnifying glass, they seem to be under a smooth surface of glaze so I agree that they may be porcelain clay impurities. 

@sharonp

I agree. The glaze over the spots seems as smooth and shiny as regular glaze. They're certainly not on the surface. 

Interestingly enough, I just got finished using hydrogen peroxide to clean my porcelain box...I will post a few pics tomorrow.  In 2 days, the dark stains on the crackle has completely disappeared, and other stains have been 99% removed as well.

So, here is what I can tell you from my experience...  

I've use hydrogen peroxide to clean Japanese prints on a regular basis, and I learned the technique from an accredited museum conservator.  So, the process works the same with porcelain, but it takes a bit longer since porcelain is not as porous as paper.

The key is NOT the strength of the peroxide... it is the exposure to UV light!

I use generic brand 3% strength peroxide.  Just fill a clear plastic container and set the object you're bleaching into the peroxide, then set in direct sunlight.  I have never tried using a UV light, but I suppose it should work.

UV light acts like a catalyst and you'll see small bubbles form on the surface of the porcelain object fairly quickly. If you see the bubbles...it's working!  If not, it might be working, but on a very slow rate and/or small scale.

Once you've achieved the desired color (or lack there of), then I suggest removing the object from the peroxide bath, and leaving the object in the sun for a few days to allow all remaining peroxide to fully dissipate from the porcelain.  I suppose soaking the vessel in water will also help to dilute and dissipate the peroxide, but I've never needed to do this with porcelain. 

However, I do soak all of my Japanese prints in distilled water in order to remove excess peroxide, sometimes twice over several days, before I dry them.  Remaining peroxide in paper can cause the paper to whiten to a level that does not look natural.

This is probably a stupid question, but I assume you dilute the peroxide? Or does it get dabbed on neat?

What about things like Vanish or Milton, will they work? Or some of the Oxygen based cleaners?

Sorry for all the questions, I am always nervous of cleaning other than soap and water but some pieces do need hairline cleaning.

Dear Greeno,

let me joke about another semantic interpretation 😊.

You said that “In 2 days, the dark stains on the crackle has completely disappeared, and other stains have been 99% removed as well.”

It is not exactly that way. The stains have not been removed in case of peroxide; they have just changed the color, but the substance is still there. It is exactly the reason why I prefer the bath with enzyme-based detergent and the water jet.

It must be considered that a hairline must be fixed. If not fixed, the crack will inevitably progress over time.

Then, after the cleaning, the hairline must be in conditions to suck the glue. If the staining substance (most of it is fat for handling) has been removed, then the glue will better penetrate and, most important, better adhere to cleaned surfaces. If the fat is still there, and just whitened, the gluing process will be less effective.

Anyway, as I said before the trick is not always effective, it depends on the type of the staining substance, but it works well in the majority of cases. Hence I suggest to try it before, being in fact simple and less dangerous, and switch to more aggressive agents only if necessary.

I am adding a picture showing the before/after the effect on a kraak dish.

As said before, note that the foot too has been whitened, as well as the chalk filling of the holes for the staples. This may not be liked by everyone, but the fact is that the technique used has not been based on changing the color, but simply on removing the dirty instead. So the appearance of the foot must be same that it had when fresh from the kiln.

Regards,

Giovanni