Porcelain marks or manufacturers marks not only tell you who made what and when, but these also indication to the standard of the piece as well. These are known as FIRST QUALITY and SECOND QUALITY.
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This is when a piece is of best quality and often indicated by a complete Porcelain mark or manufacturers mark.
This is a factory second and often sold as such by factory shops. Manufacturers always indicate these items by marking, scratching or disfiguring the Porcelain marks.
Wedgwood, Royal Albert, Paragon, Doulton, Worcester all indicate seconds by grinding out part of the mark. I have come across all these and it is pretty obvious from first glance that this was deliberate.
Advise to buyers
You will come across many examples on eBay and my advise is to purchase after examining a clear image of the Porcelain mark or manufacturers mark so you can decide if it is what you want. Remember that a piece of SECOND Quality will not command a premium and a auction that does not show the Porcelain marks will be hard to verify manufacturer, date of manufacture and standard of quality.
Advice to sellers
Always include images of the Porcelain mark or manufacturers mark not only to verify the manufacturer but also to help the buyer to date it and verify its quality. A knowledgeable buyer, if given a choice, will always go for an item with a picture of a manufacturers mark.