is there a source where i can research old china. i inherited these
plates and want to know value before i sell them. the plates are
'minton' with b878 or b848 inscribed.

Deba -ga ,

Go to the great website called REPLACEMENTS, an amzing resource on old
china.  You can type in any brand of china and get info and buy or
sell.
In the search box I typed Minton b878 and up came a plate.  They
didn't
have anything for b848.     
You log on and register (at no cost) and then you can buy or
sell and get info on prices, availability.   You can also 
talk to them by phone, from 8 a.m. to midnight, 7 days a week.
Here's the URL:

www.replacements.com  
or
1 800 737-5223

Been there done that! the pattern displayed from Replacement.com is
NOT my pattern.I need a CATALOG of old "out of service" patterns from
Minton. Is there not a resource from this manufacturer where ALL china
patterns are listed. This website you provided was already researched
by me and gave no answers to me. I searched the web for two weeks and
could not find this pattern.

Sorry, I'm not one of the researchers.  I was only posting a 
"comment."  Hope one of the registered Google reserachers can
direct you.

You need to send a link with pictures then we may be able to help. The
marks on the back of the plate need to be photographed too. Godden's
mark book and specialist books on Minton can then be used to research
your plates. There is a lot of information out there but no one can
really help without more information. There are no fixed values for
such things. Secondhand and antique ceramic prices are purely
dependant upon supply and demand virtually on a piece by piece basis.
In a posh shop you may pay several times the price you'd pay from a
jumble sale. There are different values. Purchase prices are often a
lot higher than selling prices. The difference is the profit margin of
the dealer.