Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: How easy is the maintenance on the mugs?  Is spotting and tarnishing a problem?
Document: I just discovered Moscow Mules!!! What a lovely, refreshing drink!! The ONLY way to partake though is in these copper mugs. I am so happy to discover My Kitchen Concepts brand thru Amazon. I just introduced my husband to them and he too is enthralled. He highly commented that these mugs are a perfect addition to enjoy these drinks properly. His biggest comment is how the copper keeps these drinks extra cold from start to finish. Perfect size, perfect lining, and perfect easy to hold handles.
The handle is nice and sturdy. It is easy to clean. I am very satisfied.
It not only is beautiful, but  keeps drink cold as needed. Love the thumbprint on top of handle.comes in very handy and adds to beauty of cup. Ordering and receiving were easy and fast. Really surprised. Great customer service. Thanks.
The only problem with the Moscow Copper mug is you will want a dozen of them!! It also gets a lot of compliments when I am out and about with it. I am looking forward to getting the bigger size next.
I am a big fan of Moscow Mules, the drink and especially the mug, so of course I had to find my very own beautiful copper mug for home. I am so please with My Kitchen Concepts and their mug... very simple and perfect for parties and get togethers. I plan on getting some more so that I can share my love and excitement of this awesome drink.Very fast shipping and very easy to order. Do yourself a favor and get yourself one!
Great mugs! Definitely recommend
These classic copper mule mugs not only kept our drinks cold, but are beautiful to look at!
I just received these four mugs. Great quality. Prompt shipping. Tested them out and very happy. Thanks!
The mugs came quickly and are as described. I think the lining on the inside will wear better than having copper on the inside.
Just got my new mugs and enjoying my first Moscow Mule. They are the perfect size and I couldn't be happier with my purchase.
Answer: http://gomoscowmule.com/how-to-clean-your-copper-mug-and-keep-it-as-new/