There are really too many to even begin describing all the porcelain age faking methods. It is recommended that the serious collector obtains a reference book on porcelain faking to get a detailed overview on the major known methods. This will be of some help in cases of doubt.
Below I list a number of points related to porcelain age faking that you should pay attention to when obtaining ceramics from unfamiliar sources.
How to avoid buying a fake
List of possibly faked elements to watch for:
Age faking methods employed:
artificial (painted) rust spots
prickling of glaze with a tool
scrubbing of glaze to reduce its shine
immersing in acid
even immersing ceramics in urine is reported
refiring at low temperature
smoking porcelain
burying porcelain in soil
exposure of ceramics to X-rays is reported
Look out for the following suspicious signs:
glaze too shiny for its age (note: before the late Qing dynasty the glaze was more mellow; it would not be so reflective as to be miroring objects)
glaze too dull
no scratches or crazing at all even after centuries
foot rim too dark or dirty
unglazed collar of lidded jars appears too dark
too many dark spots (sprinkled) over body, glaze or bottom
dirty, unclean look
artificially added damage, like chips or breaks
fake staple repair (new repair)
fake shards
old bottom but shiny, with unscratched glaze
bottom firing color or glaze wrong
More difficult to identify:
Decoration color not right for period (the color or underglaze blue is wrong for a specific period. Imported blue pigments were not available at times due to prohibition of overseas trading; local blue pigments had a different blue tone. Some decoration colors did not exist until later in the Qing dynasty.)
Wrong decoration The decoration content and its elements varied from period to period. The decorative design and the "musts-and-must-nots" of decoration were at times strictly regulated. Easier to identify differences are the eyes of people. They were painted differently during each reign.
Old ceramic body with new decoration The color seems not right for an item's age. The decoration was added more recently on an old piece with no or little decoration, to increase its value. more
Old bottom and new body A favorite...the fakers know that the bottom is important for deciding age. They attach an old bottom to a new body. Always also check the body glaze for age signs. The ceramic body itself might be new! more
Transplanting the mark A genuine old period mark is cut (from a shard, presumably) and embedded in the bottom of another piece.
Discoloration or soil covering part or all This shall make you believe the item was buried in the soil for a long time, i.e. that it was excavated. If an items was buried in soil for hundreds of years, it may be difficult or impossible to clean all the soil off completely. Low temperature firing is used to make new soil stick to the ceramic body to fake age.
Smoking An ageing effect is reached by exposing a new ceramic item to smoke.
Burying ceramic items An ageing effect is reached by burying new ceramics for some time in the soil.
Fake sediment and maritime growth on shipwreck porcelain Yes, even these are faked. Hard maritime growth is glued to ceramics and pottery to obtain fake shipwreck ceramics. more
Bubbles wrong Bubbles direction - manufacturing was not done in terms of single items in Chinese ceramics production , but in batches. However, as there were not mass production methods existing, items were formed one by one. Round items were thrown (turned), while rectangular and other shapes were formed in moulds. Even preparing the clay was done with manual or semi-manual methods. more
A tip: The most important part when deciding age is always the bottom. Every collector or expert will always look at the bottom to check for age signs. The forgers know this. Their porcelain age faking methods will always put the most effort into either creating a fake old-looking bottom or they attach an old bottom (from excavated shards) to a new body. In doing so, however, they often neglect the importance of the glaze, etc. for judging age. It may look much newer than the bottom. Keep this in mind when checking a piece for signs of porcelain age faking.