I typically use 1.25"  drywall screws..

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The hole in the back is at a slight angle, so the weight will pull it to the wall.

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Ideal Spacing is 2" between tiles. 

This puts screws at:

 7.25" apart horizontally

and

10.5" apart Vertically. 

(see How To video Below)

 

Yes!  Enamel is extremely durable!

 

Essentially it is glass,
so a lint free damp cloth OR
 Ammonia Free Glass Cleaner 
will shine it right back to new!
 

*Don't spray the cleaner directly on the Artwork- spray on the lint free cloth first

 

Absolutely!  I do it all the time. 
All you need is a opaque Paint Pen

 

Two of my favorite bands are
"Metallic Sharpie" and PenTouch...
but really any brand will work. 

 

Be careful tho!  If the air pressure changes, sometimes they explode

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