Hello :D

"This shirt is made of cotton."

How can I change this sentence so that it's in the active voice?

"Cotton made this shirt." has a different meaning. "Cotton was used to make this shirt." has the correct meaning, but is in the passive voice. I also have trouble with sentences like "This fork is used for eating.".

How do I go from passive to active and back again if there isn't a 'doer' in the sentence?

Thank you for your help.