Felspar porcelain has a glass like finish which made the china very popular at the time.
Spodes New Stone " data-medium-file="https://antiquedetective.files.wordpress.com/2012/10/20121008_193020.jpg? w=274" data-large-file="https://antiquedetective.files.wordpress.com/2012/10/20121008_193020.jpg? w=274" class="alignright size-full wp-image-15" title="Spodes New Stone" src="https://antiquedetective.files.wordpress.com/2012/10/20121008_193020.jpg?
Spode meat plate, c.1820, printed in Convolvulus and Sunflower sheet pattern, 48cm wide. Spode Supper Set in oval mahogany tray, c.1815 printed in Greek pattern.
w=292" data-large-file="https://antiquedetective.files.wordpress.com/2012/10/20121008_192849.jpg? w=387" class="alignright wp-image-11" style="width:215px;height:174px;" title="Spode Felspar Porcelain" src="https://antiquedetective.files.wordpress.com/2012/10/20121008_192849.jpg?
w=202&h=162" alt="" width="202" height="162" / Spode introduced Felspar Porcelain in 1821 it was called this as they started to use felspar in the bone china mix instead of china stone as it was found to fuse at lower temperature without the china miss-shaping.
J – January, F- February, M-March, A-April, Y-May, U-June, L-July, T-August, S-September, O-October, N-November, D-December.
For example A74 would be made in April 1874 Spode Felspar Porcelain mark " data-medium-file="https://antiquedetective.files.wordpress.com/2012/10/20121008_192849.jpg?
Some very early Spode pieces were not marked Spode but may have just a pattern number.