How to interpret diamond marks

1. Diamond marks



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During the period 1842-1883 the Patent Office issued a diamond mark along with the registration number when a design was registered.

Besides indicating that the design had been registered, a diamond mark offered the buyer the reassurance of knowing an item was of British design. It assured the person registering the design a degree of protection from copying.

The mark was created to identify the type of material used (known as the class), how many items were included, (sometimes known as bundles or packages), and the date of registration.

Below is a description of the marks and the means to decode them. Note that the registration number does not form part of the mark.

The diamond mark can help you to date a design and find out what material class it belongs to, but the design might still be difficult to trace. See our research guide on finding a registered trade mark.

2. Dating a diamond mark

On the diamond mark you will see that the year of registration is shown along with the month code. The correct year can be found from the year codes tables, and the month from its table in Section 3.

However, you will also see that there are two ranges of year codes; 1842-1867 and 1868-1883. By dint of detective work you should be able to determine the correct year from the design of the diamond mark and the placing of the day number.


3. Month codes

Month code Month Month code Month
A December H April
B October I July
C January K November
D September M June
E May R August
G February W March

4. Year codes

Two sets of year codes are shown. The first, in alphabetical order within the two time bands, is to assist the enquirer when deciphering diamond marks.


Year codes Year codes Year codes
A 1845 J 1854 S 1849
B 1858 K 1857 T 1867
C 1844 L 1856 U 1848
D 1852 M 1859 V 1850
E 1855 N 1864 W 1865
F 1847 O 1862 X 1842
G 1863 P 1851 Y 1853
H 1843 Q 1866 Z 1860
I 1846 R 1861


Year codes Year codes
A 1871 L 1882
C 1870 P 1877
D 1878 S 1875
E 1881 U 1874
F 1873 V 1876
H 1869 X 1868
I 1872 Y 1879
J 1880
K 1883

The second, in chronological order, is to help in identifying possible exceptions as shown below:

1842-1867 and 1868-1883

Year codes Year codes Year codes Year codes
1842 X 1855 E 1868 X 1881 E
1843 H 1856 L 1869 H 1882 L
1844 C 1857 K 1870 C 1883 K
1845 A 1858 B 1871 A
1846 I 1859 M 1872 I
1847 F 1860 Z 1873 F
1848 U 1861 R 1874 U
1849 S 1862 O 1875 S
1850 V 1863 G 1876 V
1851 P 1864 N 1877 P
1852 D 1865 W 1878 D
1853 Y 1866 Q 1879 Y
1854 J 1867 T 1880 J

Exception notes:
In 1857 the letter R was used during 1-19 September, and during 1860 the letter K was used for December. From 1-6 March 1878, W was used for the year in place of D; and G was used for the month in place of W.


How to interpret diamond marks
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