A pattern is a Numismatic item which never became legal tender.
The term is Essai or preuve in French;
saggio, disegno or Prova in Italian.
Probe in German;
prueba in Spanish;
Since Krause depend on many people from different countries it is therefore not surprising that different expressions get used for the same entity.
Pattern maybe struck when a new coin metal or design is to be selected. Since only a few pattern coins are minted, and most are melted at mint the pattern types which are not selected for circulation become very rare collectors items found mostly in mint museum collections.
Linked below are LakdivaCoin pages on eleven patterns from Sri Lanka most still unlisted in the Krause Standard Catalog of World Coins. Only the 1942 pattern has been listed in a 1995 Auction catalog. This is probably the first time details of any of these rare Lankan patterns have been published. They were exhibited at the 2002 October PAN Show in Pittsburgh, PA,USA.
In 1942 new type of coin was investigated to conserve metal for the war, A One cent pattern was struck in Black Bakelite plastic in high relief. I understand it was manufactured by a Private Firm and sent to Ceylon for evaluation. This was not viewed kindly by the Royal Mint which took action against the Firm This pattern was anyway not seen to be durable for circulation. 1942 September 8th, a bronze coin of half the original weight was selected for circulation.
A pair of TRIAL patterns were struck at the Birmingham Mint in 1965 and 1968, of same weight and Nickel-Brass alloy for the standard Five cents coin and Ten cents coin denominations which were first struck few years previously in 1963 at British Royal Mint (BRM).
A set of TRIAL patterns were struck in 1971 to select a cheaper alloy
for the Five and Ten cents coins in which the Nickel-Brass metal had
become almost half the face-value. In 1970 the Central Bank of Ceylon
had paid the Royal Mint 20% more than Face Value to Mint the Five cent
coin. Patterns were struck for both
and Ten cents denominations in
Nickel-Brass clad steel, Chromized steel, and Aluminum with word
TRIAL in raised letters (at about 2 O'clock) on Obverse.
Imaged above are the raised letters seen through a QX3+ microscope at 2400 dpi resolution.
These trials are followed by rare 1975 Aluminum Off-Metal-Strikes (OMS)
Five cents and
Ten cents denominations,
the circulation issues with year 1975 were struck in Nickel-Brass.
These Two were listed in the 2003 Edition of the Krause SCWC.
Aluminum was adopted and made legal for the Five and Ten cents coins only from the 1978 issue. Aluminum had been used for the one and two cents coins since 1963. The Mint cost was less than half that for Nickel-Brass
Retired officer T. M. U. Sallay of the Central Bank of Ceylon,
confirmed them to be official Patterns and OMS, except for the pair of
Birmingham Mint patterns which were never sent to Lanka.
According to him In 1971 the Central Bank made a detail study of the feasibility of using clad coins and found it unsuitable for various reasons. The main cause of concern was rust setting in the rim of the coin. Corrosion sets in the tropics much faster than in the colder climate countries. Further cladding be it nickel, bronze, copper or aluminum is only about 5% and would not stand long, the wear and tear.
The Central Bank started using Nickel plated steel coins for the 25 cents, 50 cents and one rupee denominations since 1996.
If anyone knows how many are normally minted by the Royal Mint of such Patterns and OMS are sent for approval to Central Bank, please E-mail. I understand from the Royal Mint that many were made but as is customary, then destroyed, none are even given to even the British Museum. I am waiting for reply with more details.
Many of the records in the CBSL were destroyed in the terrorist bombing in 1996 January. Bank Vaults are unfortunately not always the safest place for storage. These patterns themselves were saved from possible destruction at that time by having been released/gifted by CBSL many years previously.
The stories behind these Lankan Patterns is probably as colorful and controversial in Sri Lanka as those of the 1942 WWII - US patterns including one in Bakelite and the 1974 Aluminum OMS the was proposed after extensive evaluation of a number of alternative metals including Bronze Clad Steel, Chromized Steel and Aluminum Alloys.