Aluminum, stainless steel and titanium are all safe to wash in hot soapy water. Immerse then swish, I also recommend use of a toothbrush for particularly soiled items.
If your item contains leather, please only surface wash.
Brass can be washed in water but it is recommended to use polish.
Copper can stain green if wet, so a jewelry polish is also recommended.
Washing brass or copper items in lemon water is also effective and cost-efficient.