This is the 1976 6,50p.

I suppose that no-one really knows how many stamps of this type exists, if you count the different prints, color-shades, plate- and printing errors, etc.  And that is why I like them so much as it is a never ending job to completion.

Also it does not take a lot of money to build a comprehensive collection.  I have bought mine online for about 1,5 €/kilogram (on paper).  So now I have about 10 kilograms.  My beloved and much respected wife has soaked them, dried them an sorted them by face value and color (indeed: you have lots with the same face-value but different color). All the enveloppes are in plastic boxes and fill a small wall.

And now, when I am in the mood, I investigate and compare them one by one.  I do not collect them in stockbooks, neither do I print album pages.  I mount them with hinges in cheap ordners, on paper.  Hence I can add text and pictures, sometimes stamps on complete enveloppes, cards, FDC's, stationnary, etc.  

I wish I was cat, I'm afraid it will take me another eight lives to complete my search. 

                                       

An example of what I am looking for is in the difference of the pictures above.  These are details (of course) of different printings of the same stamp.  Now on the search for the printing date and the printer.

Most of the sources are on the web.  I give you one link to start with, a very good site. There are also FB-groups and blogs on Machins. Also you have Stanley Gibbons specialised catalog and the masterpiece is the DEEGAM catalog.