Very nice frame indeed. I was wondering the process and saw that each side was a solid 1 piece so I figured it was cut on the table saw. Still those steps can't be very deep as it looks to be about .75" overall thickness. Interesting frame indeed.
Steve you are right. 3/4" thick wood and the cuts just deep enough to call it a cut after sanding. If anyone is interested in the process, below is what I ended up doing.
I used the white wood 1 x 6 from Lowes produced in Finland. I first cut a 45 degree cut in the 1 x6 length wise on the table saw for a bevel going to the photo. 2nd on the miter saw made a rough length dimension 45 degree angle on each end of the 4 pieces of the frame. 3rd I used a sled on the table saw to get the right length of the frames 4 pieces. It took 2 attempts/passes to get a good fit. 4th after marking my top bottom left and right pieces of the frame I began cutting a shallow step/dado in the frame with just the blade on the table saw. With the face of the frame facing down I started on the outside cut first. It was 3/4" in from the edge cutting the top, bottom left and right, one after the other. I moved the fence in 3/4" and repeated the cut on the 4 pieces, top bottom left and right. I repeated the process of cutting the 4 frame pieces at the same distance at the same time until I was at the frame opening. 5th Glued/clamped the frame together. 6th sanded the frame from 80 grit to 220. 7th taped the inside step closest to the 45 degree opening of the frame and brushed 2 coats of the clear poly on the 45 degree bevel. 8th removed the tape sanded with 220 grit and lightly applied stain with a cloth rag. 9th sprayed a clear coat on and let dry. 10th I usually do a light sand between coats but didn't see any major nibs and with a time constraint sprayed the 2nd and final coat. After drying I used the 3m final sanding pad. 11th added the photo which was already glued to a piece of luan and called it done.
“It’s not a mistake, it’s a design feature”