Displaying sword and temperature

QUESTION: Since I last purchased my katana, I've been wondering if it's a good thing to always keep it in the saya. The reason I'm saying this is because i've heard from some people that leaving it in the saya is not always good and that I have to take it out and leave the blade under a cloth in the stand. Is this true? what are the effects if I leave it in the saya for long? And also I left it by the air conditioner for 2 hours (with the blade inside the saya still) and It was cold and I thought it would effect the blade, is this true? I hope you could help me and find the answers to the questions. Thanks for everything paul, you've always helped me in the past.

ANSWER: It's true that storing a Katana for a long period of time in its (lacquered) saya will cause the steel to 'sweat' as environmental conditions change, especially if the weather is humid/hot. This is why for long term storage, a bare Katana blade was traditionally stored in Shirasaya (lit 'white scabbard') - which was unlacquered and allows the steel to 'breathe'...

However, displaying a sword WITHOUT the saya can also be troublesome, as particles of dust can get trapped on the blade, absorb any oil, and create nasty splotchy rust spots along the surface...

So, there are two solutions.

The first is to use Renaissance Wax or a similar product on the sword and display it in the open.

The second (and IMHO) better option is to display the sword in the saya, but check on it periodically (especially on hot and humid days) to make sure that it is protected by a fine layer of oil at all times. As long as the oil has not dried up, the sword will be fine...

As to airconditioners making it too cold, not a problem. You'd have to have it going so cold that you'd literally turn into an iceblock yourself long before the sword was bothered by it ;-)

Hope this helps!