Here is a repost from last year about how I made my orange slice ornaments:
One of the things that was new to me this year was making ornaments from orange slices. I will be doing this again next year.I love the way the look on the tree,they add a lovely primitive look. When a tree light is right behind a slice,it looks like stained glass. Unfortunately,I couldn't capture that on film.
If you would like to try this next year for your tree,here is how I did it. I used an oven.Never having used a food dehydrator before,I wasn't sure what temp or length of time I should use,so I didn't go that route.I didn't want to shrivel the slices,just dry them.However,it does take a good bit of time:5-6 hours,depending on how much juice you can get out of the slices before you put them in the oven. It's a good project for a day when you are doing other things in the house.
Preheat your oven to 170 degrees (this was the lowest temp my oven would allow).Cut oranges into 1/4" slices. Put the slices in between paper towels,and press down on each slice. I had to use several pieces of paper towel,and there was still a good bit of juice in the slices. Do what you can. I burned the paper towels in the wood stove,so there was no trash.