Topic: Richardson's vitrified? is the vitrified referring to only opaline glass or...

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... or was the name 'vitrified' a range of different types of glass?
I've just been having a look around and came upon this jug in the Bristol Glass Museum website.  It says on it that the bottom is engraved in red 'Richardsons Vitrified' ... but the jug doesn't appear to be opaline glass to me    Not entirely sure how something can be engraved in red, but maybe they meant enamelled?
http://www.museum.bristolblueglass.com/gilt-and-enamelled-green-ground-jug-ca-1847-50/#.Unkk1PnIZqN

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http://collections.vam.ac.uk/item/O3127/jug-whb-j-richardson/
ah, this might answer my own question.
This piece is white opaline with an enamel painted decoration on it,  marked on the bottom of the jug " 'RICHARDSON VITRIFIED ENAMEL COLOURS', printed "

These two pieces are also clear glass, enamelled decoration and have Richardson's Vitrified enamelled on the base as well, so the Vitrified applies to the enamels they used for decoration, not the opaline glass that also sometimes carries this mark.
http://collections.vam.ac.uk/item/O6277/water-jug-whb-j-richardson/
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