Change in Copper trading-in bonus

[QuickTrick]

Copper trading-in bonus of -20% Recruitment Time is very insignificant (compared to all other bonuses). Have you considered changing it to something else or changing the values? Copper has plenty of uses, but in my opinion it is generally connected with gunsmithing (and maybe coins and jewellery) in this game.

One of the common uses of copper was artillery production. According to what I read on Wikipedia the more popular use of metals in artillery production was copper, at least in the early periods of the game (I didn't read about the later periods) due to some reasoning connected to durability in that period (when metallurgy was not advanced enough). Casting copper is said to be easier than casting iron in the early period of this game. Copper cannons were more resistant to corrosive effects, so they were also a popular choice on naval vessels or when used as a sign of prestige.

Do you think copper should be connected with artillery? Does it make sense to make it a sieging bonus (durability would be considered a sieging or combat bonus, due to the increased artillery fire range; it could shoot heavier projectile)? Should it be artillery cost (durability and resistance to corrosive effects)?

 

[DukeLeto42]

I'd put in a vote for artillery cost, as a corollary to the cav cost from livestock.

 

[QuickTrick]

The corrosive processes of iron, that changed iron into rust, caused iron cannons to be less durable than bronze cannons in terms of longevity. This meant that iron cannons (of similar design) could shoot heavier projectiles only for a short amount of time after the production process, considering the material was of good quality.

Plating was an invention of early 1800s, when nickel could be used in artillery (chrome plating is early 20th century). It protects from corrosive effects.

Iron ores contain oxygen element. Some of them also contain hydrogen.
Coal has different amounts of sulfur in it and iron sulfide causes defects. Sulfur makes molten cast iron viscous. Its melting point (1194 °C) is very close to grey cast iron melting point (1260 °C). Grey cast iron (graphite is formed, which is very fragile) is more fragile than white cast iron (improved hardness). Iron melting point is 1538°C.