I sew a lot of fantasy clothing. It was inevitable that someone would ask for a robe based on the Harry Potter movies. These are merely my own robes with an iron-on patch of my own design, so they're not exactly what you see in the movie. But they are made of a nice poly-cotton blend and designed with a clasp for durability. You can really have any color combination, but the most popular are on this page.
A black robe with a patch applied, this robe can be used as a standard wizard robe. You can always turn it inside out to hide the patch, if you so desire.
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Who doesn't love Gryffindor? Of course, this is just a standard robe lined with red or burgendy (depending on what the customer asks for), but it does the job.
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And Hufflepuff.
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My personal favorite is Ravenclaw.
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But the most requested has got to be Slytherin. I seem to make these all year round.
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Looking for a wizard robe you can play sports in? Then these are for you. A variety of colors are available. These robes are often used as Quidditch robes at parties. Gryffindor is a popular choice. Name and number can be added to the back, though most people leave it blank. Available in red or burgendy, depending on the whims of the customer.
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And don't forget Slytherin. I don't have any pictures of the other color combinations.