Published on 11/03/2026 · by Leandro Caldas, glazier, founder of Routeck and creator of the Arena
Mirror cutting template: the flipped pattern mistake from EP3
A mirror cutting template looks simple until the day the numbers are right and the piece still does not fit. That is what happened to Janael in challenge 3 of Arena do Vidro. He measured, he cut, the mirror did not crack, and at the judging he said the line every glazier should write down: “I went by the measurements, but I got the mirroring wrong.” The pattern came out flipped compared to the template.
This post is only about that mistake: why a tape measure does not catch a flipped pattern, and what I check before scoring. The full EP3 is at the top of this post (audio in Portuguese), and this scene is around the 11-minute mark.
What happened at the judging
The rule was to cut one of two shapes by hand, matching the template, without touching it, in 20 minutes. When time ran out, the judges went to Janael’s mirror. Natan showed there was a lot of extra space in some spots, and the conversation came down to this: “what was left over here was missing there.” Then came the comment that explained it all: “that’s what we were saying about the reflection.” And one word: “flipped.”
During the check, the judges read the same number more than once, 28, and then someone said: “the measurements must be right.” That is when Janael confirmed he went by the measurements and got the mirroring wrong. He also told the rest, laughing: he started drawing the other model, the curve got too sharp at the top, he saw it looked more like the second shape and went with it. “That’s the truth,” he said. “That’s how good I am at drawing.”
Why measuring does not catch a flipped pattern
From here on this is shop reasoning, not something said on the show. A shape and its mirror image have the exact same measurements: same width, same height, same distance between points. So the tape says everything is fine. The only thing that changes is the side.
On a rectangle, a circle or a symmetrical oval, that makes no difference. On an organic mirror, which is not the same on both sides, it is a wrong piece. Lay one over the other and the wide part of one lands on the narrow part of the other: extra on one side, missing on the other, which is what the judges described. The episode does not show the moment Janael’s drawing flipped. It only shows that it did.
Where a pattern usually flips
- Template turned over. Paper and MDF look about the same on both faces. With no mark, it flips and nobody notices.
- Wrong starting point. You measure from the left of the template and mark from the right of the glass. Every number is right and the whole shape comes out reversed.
- Drawing on the wrong side of the mirror. If you mark the shape on the paint backing and then look from the front, you see it reversed.
How to use a mirror cutting template without flipping it
- Mark the template first: write “front” and draw an arrow pointing up.
- Pick the point that gives the side away, like the widest part or the tightest curve, and note which side it is on.
- Always use the same starting point. If you measured from the bottom left corner of the template, mark from the bottom left corner of the glass.
- Work on the glass side, with the template face up. You score on the glass side, never on the paint.
- Before the cutter touches the glass, look at the template and the drawing side by side, in the same position. Is the wide part on the same side? It takes seconds and costs less than a sheet.
In your glass shop nobody forbids touching the template, like the challenge did. Put it on top and run a marker around it. With the front facing up, this mistake almost goes away. And if the customer orders a pair of mirrors, one for each side, then flipped is the order: just turn the same template over on purpose for the second piece.
What about on the machine?
In that same episode I said that with the Router Glass, a mirror like that would take me about a minute, cutting by myself. The shape comes from the file, so the step of transferring the drawing by hand is gone.
- What is a flipped template?
- It is when the drawing comes out like the template’s reflection: same measurements, opposite side. In EP3, Janael admitted he went by the measurements and got the mirroring wrong.
- Why don’t correct measurements prevent a flipped pattern?
- Because a shape and its mirror image have the same distances. Measuring checks size, not side. To check the side, use a front mark and compare with the template.
- Does this happen with every shape?
- It only matters on shapes that are not the same on both sides, like organic mirrors. On a rectangle, a circle or a symmetrical oval, the flipped piece looks the same.
Want to talk about cutting mirrors in your glass shop? Message me on WhatsApp at +55 31 9095-8383. And if you want to show your method at the bench, applications for the next season of Arena are open here on the site.
Full episode 3 · Transfer pattern to glass: why EP3 banned touching the template · How to cut a round mirror: circles and quadrants from EP3 · Router Glass
