The making of Stone Edge

I have been inventing types of pizza ovens for over a decade and every time feels like the first time!

2 years ago

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A few weeks ago about a dozen friends asked for recommendations for a small pizza oven to purchase.

Some of them even spurred a series of posts on the making of a yard pizza oven which resulted in creating a brain dump of all I know about the subject.

One of those conversations was with my friend Deborah in our backyard. While I was listing the pros and cons of those reasonably priced ovens I had a flash of making one that would fit a regular American range for a third of the price of those popular ovens like Roccbox or Ooni.


Two physicists while in Rome wondered how quickly and delicious the pizza was done in Rome. So in a true scientific fashion, they decided to analyze the secrets of the perfect pizza and even concocted a thermodynamic equation. When in Rome...

They determined that the secret of a great pizza is the brick oven. No @#$1 you might think and you might be right 😃

In a series of thermodynamic equations, those researchers determined the formula for exactly how the brick oven imparts the perfect amount of heat to the pizza. In general, heat is released relatively slowly from the brick, causing the crust to crisp up without burning while the toppings cook more quickly and give off some of their moisture, leading to the perfect balance.

For obvious reasons, not everyone can build a brick oven therefore too many end up baking their next pizza into an electric range using either a baking sheet or a pizza stone. The same researchers have tried to convert the perfect pizza formula for an electric oven with a metal surface. Because metal conducts heat so much more quickly than ceramic bricks, cranking up the oven to over 600 degrees would simply produce a charred pie.

If you are interested in the burnt pizza story, Quora has just what you need to satisfy your curiosity while your pizza burns up, have a look.

A pizza cooks simultaneously from above and below -- the dough via thermal conduction from the bottom of the oven and the toppings by thermal radiation from the air. For the perfect pizza, the cook must balance the two so that the dough and the toppings finish cooking at the same time. For that, they need to get the oven temperature right.

So the bottom line is that your electric range can't, as-is, simulate heat transfer and radiation to what a traditional red brick naturally does into a brick oven. However, while I was talking to Deborah I had a flash of why a pie cooked in a range comes out very toasty at the bottom and close to okay on the top.

A typical pizza you normally experience in a restaurant with a brick oven stays soft after it has been cooked. Essentially, you can bend it. The one you cook into an electric range becomes stiff and it overcooks the bottom releasing all moisture that makes the dough foldable.


The essential reason for this excessive "toasting" is that the synchronization of the thermal conduction and thermal radiation. for the lack of a better term, is out of sync. Let me explain in a more practical matter:

You already had your good share of failures with backing sheets, so you wised up and bought one of those stones for pizza that your friends so much talk about it. To increase your chances of a better pizza. You warm up the stone as per instructions, then put your raw pie on top of the stone and closed your range's door.

Every now and then you turn on the range's light and take a peek at how the cooking is going. And here is the critical detail, unless you have developed hyper vision sight, you are looking at the top and can't look at the bottom of the pie like a pizzaiolo does use the peel. Therefore, you judge when the pizza is ready based on that point of view. Because the thermal conduction at the bottom is out of proportion higher to the thermal radiation on the top. The bottom gets overcooked while the top stays raw-ish. Giving the overall finished product a higher crunchy consistency than what you normally experience in a pizzeria. And that affects a lot your ultimate comment after the second bite of your last beauty: not bad but not the same as the real thing.

While I was talking to Deborah all that flow of knowledge twisted into my head at the same speed that I ride downhill from RR trail with my Evil Black Mamba. If you are not a mountain biker, I was thinking very fast...

My conclusion is:

Since you can't recreate the thermal radiation of a brick oven, you can create a (logical) thermal vacuum on the top of the pie which should reduce significantly the thermal distribution and impact on the raw dough than just...the convection air. In order words, you increase the heat on the top to accelerate the toppings cooking speed to come as close as possible to what is happening at the bottom.

After Deborah left, I kept thinking about variations of the concept, and in a moment of being stuck in the bed (a seasonal cold) I grabbed my iPad Pro and my Apple Pencil and jotted down this.

As I was sketching I got really excited about how something this straightforward could actually make a noticeable difference. After the sketch was done I bought three stones, one rebar of 1/4in thick, and yesterday they were delivered to my doorstep.

Let's build it!

Today, (Sunday, in the US) I woke up with the intent of building the thing. Here is what I did to make it.

The stone is about 15 x 12 x 0.63 inches and weighs 6.5lbs. Overall weight was a concern so I didn't want to add too much pressure on the range's grids, therefore I set to create the most minimal structure I could to hold the parts together. Ultimately you can lay the structure on the floor of the range, my preferred option, but I wanted to leave room for multi-usage options.

I cut four pegs (feet) for a length of 4 1/8 (10.795 cm)

and two bars for a length of 15 1/4 (38.735 cm). At the bottom of the pegs, I welded a washer of about 1 in diameter.

Then I welded the bars to the pegs and checked that the stone was in level. I don't have a metal cutter to be very precise with the cuts and the grinder takes a bit of skill to minimize the error for a similar outcome that a metal saw would produce.

However, judging from this photo below, I got that skill. Achievement unlocked!

The next objective was to figure out how to hold the side walls in place without too much metal that could disrupt the brick-only confinement I was aiming for. I used two bars of 11 3/4 (29.845 cm) long, 1in high, and 1/8 thick. I curved the opposite corners of the bars to lock in place the bottom stone and the walls.

The idea is to make it simple to separate all parts for easy storage but at the same time to secure the locking of the parts to avoid that they would come out of their sockets while loading the pie.

The pegs have been aligned to avoid the heating element at the bottom of a range and the height to raise the base enough to meet the base of the range's glass door. I wanted to make it higher but I didn't have enough metal so I compromised. It is the first prototype so making it coming this high in quality is already a craftmanship achievement.

It was time to measure the height and constraints of the walks. In order to make them lock without requiring any thermal glue (!) or other locking materials that would have made all usage operations clunky. I cut two notches on the corner of the wall. Enough (1/2 in / 1.27 cm) to make the wall sink in and make it rest on the rebar. The wall would be constrained by the bottom tile in one direction and held tight by the metal bar on the external side.

It went in very snag and tight enough to not fluctuate. I left minimal room for allowing thermal expansion. This material doesn't expand on its own, however, over time as the food release moist and grease, the material adapts under thermal fusion, effectively making it bigger.

Couldn't resist... 😃.

The walls were up and stable. No was time to lay on the top, the upper wall. It just rests on top of it and because the material has high viscosity it doesn't sleep. Plus, the 6.5lbs of the tile make it stable for the job. Easy to disassemble and adjust at will.

I was very pleased with the outcome. I then used some heat resistant paint to make it look like the Ferrari of the Stone Edge oven in the oven - basically the thermal version of an Escher's painting.

After the paint dried I did a heat test to make sure that the paint was well cured and didn't make any smell. It didn't take long to realize that when looking at small characters in the back of a can of paint, I should have used appropriate lighting and definitely reading glasses! I grabbed the wrong can and the paint wasn't heat resistant. The can next to it was it... Getting old sucks beyond getting a few wrinkles on the face...

Scrab, clean, a few Italian swearing words, and then the proper can of paint to resume the testing. The wife was unaware of what I was building so I used her no prior knowledge setting to test the assembling phase. The markings on the edges led her to figure out what went where and it went very well.

It's like LEGO met MARIO BROS and they had a child called Stone that lives on the Edge.

She tested first on the countertop to figure out the sequence of the parts and then proceeded to assemble it in the range. Fired up the range to pre-heat the parts and in the meanwhile crafting the dough "balls" to be backed.

While she was assembling, she realized (I didn't and it wasn't in my design intentions) that you can bake two pizzas at the same time. One in the center and on the top for those who like the old "mattonella" style.

I then charged up my FLIR and prepped everything for heat distribution analysis.

When loading the pie in Stone Edge (so I nicknamed it) I recommend not using a square peel but a rounded peel that is 30% smaller than the surface of the upper tile. That will make the insertion and eventual turning a lot easier.

In the next post, I will share the thermal results, a video demonstration, and some pizza testing. That will be the hardest part, eat all that pizza, for science...

;mE Out.

Mario Esposito

Published 2 years ago