The 2016 Annual Report Part 02 Accounts and Operations of the Central Bank of Sri Lanka §5.2 Currency Printing and Minting
In 2016 the Currency Department has taken steps to reduce the cost of minting coins by changing the metal type of Rupee 1 and Rupees 5 coins (minted after 2005) from brass plated steel to stainless steel.
Further, arrangements were made to design a new set of circulation standard coins from stainless steel metal for the denominations of Rupee 1, Rupees 2, Rupees 5 and Rupees 10 reducing the sizes of coins with the objectives of reducing the cost of minting and easy handling.
CBSL Governor Dr. Indrajit Coomaraswamy on 2018 January 3rd in presentation of the Road Map 2018 said,
We are also planning to issue a new coin series in 2018 by changing the metal of the coin, which would reduce the cost of minting, while also increasing durability.
In the medium-term, we intend to establish a state-of-the-art cash center to improve currency operations. Also, plans have been made to set up coin dispensing / recycling machines island-wide to smoothen the distribution and recirculation of coins in the country to meet the demand.
Based on documents I found online I was able to estimate average cost per coin of minting 2016 and the new 2018 coins
The 2018 coins will add about 48% to the value of the Rs11,355M of these coins in circulation as of 2017 August 31st.
I suspected from the cost of Minting coins that all of the coins ordered in 2017 March are smaller, and that was unofficially confirmed. As this is the case, 2016 Re 1, Rs 2 and Rs 5 will be 1 year types. The total cost of Minting the 970 Million coins is less than then 50% of Face value. However the Re 1 and Rs 2 coins still cost more than face value to mint. They could have switched them to Aluminium which would have also aided their identification.
In 1940, 10 rupees was the value of a gold sovereign. The Sinhala term "Silima" for the British denomination shilling was 50 cents. At the time the 10-rupee coin was introduced in 2009 a gold sovereign cost more than Rs. 30,000. It is ironic that all our coins have a buying power less than the half cent coin when it was demonetized in 1941.
After 2018 coins are issued, probably in early 2018, coin change in Sri Lanka will be a total mess, as many types of coin sizes of each denomination will then be in circulation.
In my opinion they should go to the size and shapes of the 1, 2, 5, 10 cents coins minted in 1963 in Aluminium and Brass and since 1978 in Aluminium. The value of the current Sri Lanka rupee is the about the same as the Sri Lanka cent during that era. Around 1970 a Gold Sovereign was worth Rs150 and now over Rs50,000. A factor of over 300.