Pottery made to order | repair and restoration studio in Southern Delaware
Restoration studio in action

Safely Removing Staine Crazing Lines and Discoloration From Porcelain. Pottery and China

Broken Ceramic Repair Lessons
(click pictures)

Fixing broken plate lesson - basic lesson
Cementing only lesson
Fixing chipped Italian platter lesson step-by-step lesson
Chipped pottery repair lesson

kintsugi - mending broken pottery with gold
Kintsugi - mending with gold
How to Replace Stoneware Crock's rim using the potter's wheel
How to replace Stoneware crock's rim
Cementing, filling, coloring and glazing broken antique plate
Restore plate lesson including coloring
kintsugi - mending broken pottery with gold
Kintsugi - mending with gold
How to repair crack in ceramic
How to fix ceramic crack
Restoring multi breaks and missing piece antique bowl
Restore bowl lesson w/ missing pieces
Cybis Arion Boy on Dolphin - Repair Broken and Missing Finger
Miniature repair w/ missing finger
Restoring ceramic sculpture with missing pieces using fired clay
Making missing part w/ fired clay
Repairing broken stone sculptures and statues
Repairing broken stone sculpture
How to paint broken china, ceramic or pottery?
Painting pottery after repair
Restoring ceramic sculpture with missing pieces using fired clay
Sculpting missing pieces
Restoring ceramic sculpture with missing pieces using fired clay
Bronze sculpture repair

We regularly receive repair estimate requests asking us to clean pottery and porcelain to eliminate contaminated discolored crazing lines and stains. These stain marks are typically form in older vintage china or antique ceramic objects. For reasons we will explain below, we do not take such tasks on but thought it will be useful to provide the information you may want to know if you choose to remove these stains yourself.

What are these stains or Discoloration on pottery?

stained crazed lines on old pottery
Stains along glaze crazed lines

stained dirty antique pottery / china
stain spots



damaged pottery due to improper cleaning
Possible flaking damage

Stains occur due to seepage of moisture through very small (and sometimes invisible to the naked eye) cracks in the glaze often referred to as crazing, crackle or pin holes in the glaze. The penetrated moisture combined with organic matter (Tea & coffee, oil, fat, food, dust, etc.) evolves into a bacteria that typically is brown or black in color present between the glazed craze lines or in the clay body under the glaze. Therefore, scrubbing the surface will not help. Bacteria stains are more likely to occur on earthenware or stoneware type pottery due to the ceramic higher porosity level allowing the moisture to penetrate deeper and stay wet creating perfect enjoyment for bacteria to flourish. High fire ceramic such as porcelain, which has almost no porosity, will less likely stain.

What is crazing / crackles and why do they happen?
They are a network of lines or cracks in the fired glazed surface. They usually occur at the end of the kiln firing process when the outside surface cools before the clay body under the glaze cools. Crazing can also happen during the vessel’s life time due rapid temperature changes (day/night, hot water / cold water, etc.). Often, for aesthetics reasons, the crazing effect is introduced on purpose on Japanese, Chinese or Raku dishes or vessels – see examples below which this cleaning instructions does not apply to. More about crazing

raku crazing
Crazed glaze implemented intentionally:

What NOT to do?

1) Do not use bleach or chlorine. Bleach or chlorine may remove the stains but also can damage your ceramic item as illustrated below.

2) Do not heat in oven. If the stain is old oil based substance (e.g., grease), it can melt and spread under the glaze creating a larger stain.

3) Do not go through the described process below if the item requires cleaning has a repair. The repair will be damaged.

What to do? Easy way for mildly stained pieces:
Buy regular oxygen bleach typically used for laundry (e.g., OXY), mix the powder in hot water and wait for it to cool off or use the liquid version of oxygen bleach. Soak your stained item in the solution for several hours or until you see the stains disappear. **

What to do? More involved and more effective process:
From a pharmacy or a beauty supply store, purchase 8% Hydrogen peroxide bleach that is typically used to bleach hair. Soak your stained item in the solution for several hours. Then, while wet place it in an oven and set to 180 to 200 degrees Fahrenheit (82 to 93 Celsius). Let the oven rise to 180-200 degrees F * while your item is in the oven. WARNING: Do not enter your item to a preheated oven. The rapid temperature change could crack the item or chip off some of the crazed glaze. After 30-60 minutes, take it out, wait for it to be cooled to room temperature and wash it with room temperature water. You will see slightly colored water seeping out from the crazing washing off. **

* Warning - Heating to above boiling temperature may results in organic matter burn stains

** While this removes the color it does not remove the foreign matter (dirt etc.) causing the stain, thus, stain can reappear if introduced to moisture.

WARNING!! Using a stronger solution of peroxide is extremely dangerous. It can burn the skin off your hands and cause permanent damage to mucous membranes, and unless you know chemistry very well you could have an explosion. Leave the work with stronger hydrogen peroxide to the professionals.

What if the stain is not eliminated?
For stubborn stains, you will need to repeat the above process every 24 hours using fresh materials each time. The above mentioned products are effective only about a day once in a liquid form exposed to light.

Why we do not take on such projects?
1) The results are not guaranteed and not 100% predictable.

2) Possible glaze flaking could occur

3) The above process may not remove the material that caused the bacteria / mold in the first place, and it's possible that same contaminant will reappear.

4) Bleaching may not remove inorganic stains such as rust or other clay minerals (Calcium, Lime, etc.) contaminant marks. In this case the stain must be removed requiring elaborate repair and restoration effort.

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