Author Topic: An Open Call to Ceramic Engineers- Reverse Engineering Biscotto di Sorrento  (Read 15247 times)

0 Members and 1 Guest are viewing this topic.

Offline Tscarborough

  • Lifetime Member
  • Global Moderator
  • *
  • Posts: 3855
  • Location: Austin, TX
    • Pizza Anarchy
Re: An Open Call to Ceramic Engineers- Reverse Engineering Biscotto di Sorrento
« Reply #50 on: February 28, 2013, 11:21:26 AM »
Pretty much.  I have fly ash and access to a different type of tufa, maybe I will make a mix.


Offline misterschu

  • Registered User
  • Posts: 278
I'm planning to build a new pizza oven out of castable refractory in May so I've been looking at oven floor material, which seems to me to be very important and very hard to get right.  My past experience has shown that conventional firebricks are way too conductive.  For this effort I've been emailing some refractory manufacturers.  I emailed Plibrico and got a very positive response from them, though I'm unsure of the strength of these bricks.

Seeing that Biscotto di Sorrento is mentioned as having .3-.5 W/mC, Plibrico has two domestic firebrick options that are in the proper range. Can anyone advise on the durability of these?  I've uploaded the datasheets showing conductivity below, and linked the the MSDS on their site here: http://plibrico.com/uploads/MSDS/msds%20Pli-Bric%20IFB%2023%20%2026%20%2028%20%2030.pdf

Offline shuboyje

  • Registered User
  • Posts: 1242
  • Location: Detroit
Those are insulating bricks, and as such don't have near the mass you want for an oven floor.  They are 55 pcf density, my quick calcs say standard firebrick at about 8 pounds is around 151 pcf.  If you are already going the firebrick route, whitacre greer low duty fire bricks have proven to be the best choice, the only downside to them is you can't get them is large tiles.
-Jeff

Offline vtsteve

  • Supporting Member
  • *
  • Posts: 458
  • Location: Vermont, USA
In addition to the lack of mass, IFB is very soft and friable; it wouldn't hold up well to contact with peels/firewood/brushes.
In grams we trust.

Offline sub

  • Registered User
  • Posts: 737
  • Location: Belgium
Hi

From my research the Biscotto is only composed of clay and water, hand pressed and dry for few weeks.

Forni Aversa: la lavorazione

Biscotto means first cooking (but not vitrified) in pottery, they fire the clay around 800C -1500F

Come Trasformare L'Argilla In Biscotto

The thickness is 5cm or 2"


Offline sub

  • Registered User
  • Posts: 737
  • Location: Belgium
In the pictures, you can see impurities in the clay which make me think it's dug and used as is and not refined.

Biscotto from Aversa

scott123

  • Guest
Biscotto means first cooking (but not vitrified) in pottery, they fire the clay around 800C -1500F

American potters use the term 'Bisque' or 'Biscuit.'  I wasn't ware that BdS wasn't vitrified.  As far as I know, cordierite and firebrick are always vitrified.  I can't help but wonder how the lack of vitrification impacts moisture in the exterior pizza crust as well as conductivity.

We've tested the absorption of vitrified ceramic materials (cordierite/firebrick) side by side with less porous materials like soapstone and steel, and the differences seemed fairly inconsequential, but the porosity of unvitrified ceramics is another story completely.

If BdS is truly unvitrified, then if you maintained a puddle of water on top, eventually, the bottom of the stone would weep with moisture. I'd be interested to see if this could be achieved.

As far as conductivity goes, this could be the missing link in understanding why BdS is so low compared to other materials.

In the pictures, you can see impurities in the clay which make me think it's dug and used as is and not refined.

Tom may be better able to address this, but it's my understanding that, for most industrial applications, clay is used in it's natural state.  That being said, aggregates are almost always added to clay in these types of applications, so the particles you're seeing in the photos most likely are added aggregate.

Offline sub

  • Registered User
  • Posts: 737
  • Location: Belgium
As far as conductivity goes, this could be the missing link in understanding why BdS is so low compared to other materials.

The weight, they're light from what I've heard. 


Also the firing temperature can change the end up product from what I've learn about pottery:

Quote
The temperature a clay is fired to makes a tremendous difference. A clay fired at one temperature may be soft and porous, while that same clay fired at a higher temperature may be hard and impervious. 

From Aversa website: 
Quote
Prima di essere cotti nell'antica fornace a legna a 800 gradi, i mattoni vengono messi ad esssiccare per qualche mese nella stagione estiva, due nel periodo invernale.

Antonio Mastroianni   (another Biscotto maker from Casapulla) fire them at 930

Quote
Dopo la formatura, vengono messi ad asciugare a temperatura ambiente, dopo asciugato vengono inseriti nel forno a legno e cotti  all'incirca a 930 C.


« Last Edit: July 05, 2014, 05:40:50 PM by sub »

scott123

  • Guest
The weight, they're light from what I've heard.

The supposed conductivity range of BdS posted earlier in this thread matches up with that of insulating firebricks.  BdS is light, but it's no where near insulating firebrick light.  There's more going on here- the lack of vitrification.

As you look at American firebricks and commercial WFO hearth materials, the choice seems to break down, across the board, to either vitrified ceramic or cast cement. That could very well be the reason why Americans can't find a domestic product that matches up to the Biscotto specs.

This knowledge could, to a small extent, open the door for someone interesting in making BdS domestically.  This is probably going to raise Marco's blood pressure ;) but I'm pretty sure a domestic analog clay could be found.  I'm not saying anyone with a kiln can do this- I've tried making molded ceramic tiles in the past and getting a final product that's perfectly flat is close to impossible. For the right person/people, though, there's a chance. This forum has seen potters/ceramic engineers in the past, but, unfortunately, none of them are presently active.

Still, though, I think there could be a market for this.


Offline sub

  • Registered User
  • Posts: 737
  • Location: Belgium
The weight for a stone of 34,5x40x2,5cm is 4.7kg.

ps: It may be not very accurate, the thickness vary a Little, they are made by hand after all.

I will try to make a sample at home, I've dug up some clay,  used water extraction and let it dry, but the plasticity wasn't right, too much fine sand in it, I've screened it again, now it's drying hanging in a cloth bag.

For the kiln, this may do the trick:



scott123

  • Guest
Chris, that video is for a raku technique.  The temperature is too low and too uneven for your purposes. You can't do this without a proper kiln.

I applaud your initiative, but digging up some clay is not the answer.  Your best bet is to do further research on the clay used in biscotto, and then purchase a clay that matches those specs. For instance, if they're using a clay that sinters at 800 C, then you'll want a clay that sinters at 800 C as well.

Offline sub

  • Registered User
  • Posts: 737
  • Location: Belgium
Well, I' ll try anyway, I don't want to buy clay.

I can past the quartz inversion stage, in my electric pizza oven     ::)

Here is a video of Marcello Aversa, from his website he fire the clay at 920 - 1688F



I don't think he bought it, he's very traditional in his approach.

The biscotto must be undercook on purpose, there is no way they built ovens with a floor who need to be changed often without a reason behind it.


A COMPARATIVE STUDY OF MINERALOGICAL TRANSFORMATIONS IN FIRED CLAYS

scott123

  • Guest
Chris, I'm not sure if you're joking or not, but you can't use your pizza oven to fire clay :)

Different clays have different sintering temps, but 800C is about as low as you're going to want to go. That's 1472 F.  Your oven isn't going to hit that, and, even if it could, it couldn't maintain it evenly over the course of a few hours.

Kilns are highly specialized equipment.  They're insulated in such a way and have thermostats that regulate the heat so that they heat up very gradually and evenly over long periods of time (a day or more) and then cool down just as gradually.  It's this very gradual heating and cooling process that prevents your pottery from cracking.

If you watch the video you just posted, almost every shot captures an incredibly traditional approach- from appearances, almost everything you see could be from 500 years ago. The sole exception, though, is the brief shot of the kiln. That's a very modern/technologically advanced kiln. I don't recall seeing any shot of Biscotto kilns- most likely because they're not as timeless looking as the rest of the process.  I guarantee you that they're using modern equipment.

You've uncovered some important pieces of the puzzle, but, if someone's really going to reverse engineer these, they're going to need some serious ceramics background and equipment.  No offense, but it's not you- nor, for that matter is it me. Over the years, I think we've had members with the necessary background, so, hopefully we'll get someone with that kind of knowledge again.

Offline Hickory.Bill

  • Registered User
  • Posts: 10
  • Location: United States
  • I Love Pizza!
Have you considered a clay bonded fused silica.  Close in density and hardness to corderite (cheap pizza stone) but extremely thermal shock resistant. can easily go from 800F to ice water. Good to a use temp of 2200F.

Bill

Offline TXCraig1

  • Registered User
  • Posts: 16248
  • Location: Houston, TX
    • Craig's Neapolitan Garage
Have you considered a clay bonded fused silica.  Close in density and hardness to corderite (cheap pizza stone) but extremely thermal shock resistant. can easily go from 800F to ice water. Good to a use temp of 2200F.

Bill

The key requirement is extremely low conductivity not thermal shock resistance.
"We make great pizza, with sourdough when we can, commercial yeast when we must, but always great pizza."
Craig's Neapolitan Garage

Offline Hickory.Bill

  • Registered User
  • Posts: 10
  • Location: United States
  • I Love Pizza!
The key requirement is extremely low conductivity not thermal shock resistance.

Ok, they you need to go with a composite system.

This is how high temperature refractory kilns are constructed.

The walls and ceiling are made from IFB, (insulating fire brick) as other have mentioned.   The deck is made with IFB and topped with a hard deck tile.

This photo shows loose fill, but it could be IFB.  It also shows piers to hold the weight.  Definitely needed if you have loose fill, but not for an IFB base if your not loading a lot of weight in.


Offline shuboyje

  • Registered User
  • Posts: 1242
  • Location: Detroit
Completely different then a kiln.  The oven floor directly contacts the pizza.  Therefore the thermal conductivity of the material that the pizza bakes on is incredibly important.  Any oven worth a darn has a composite construction with a dense floor and dome backed by a insulating layer.  What we are after in a specialized material for the inner layer of the composite system that will contact the pizza.  It needs to be suitable to serve as a hot face in a wood fired oven, but also needs to have a thermal conductivity of about 0.6 and currently it is not available in the american market above brick size.
-Jeff


Offline Hickory.Bill

  • Registered User
  • Posts: 10
  • Location: United States
  • I Love Pizza!
Completely different then a kiln.  The oven floor directly contacts the pizza.  Therefore the thermal conductivity of the material that the pizza bakes on is incredibly important.  Any oven worth a darn has a composite construction with a dense floor and dome backed by a insulating layer.  What we are after in a specialized material for the inner layer of the composite system that will contact the pizza.  It needs to be suitable to serve as a hot face in a wood fired oven, but also needs to have a thermal conductivity of about 0.6 and currently it is not available in the american market above brick size.


Ok then, how about a castable. Then you can make any shape you want.

Here is a fused silica castable that has a conductivity of 0.69 W/mK @ 600C.  the conductivity would be less at lower temperatures.

http://www.morganthermalceramics.com/sites/default/files/datasheets/1_fused_silica_cast.pdf


Or this one made from Calcined Fireclay with a conductivity of 0.72 W/mK @ 600C.

http://www.morganthermalceramics.com/sites/default/files/datasheets/1_hs_cast.pdf



And for lower conductivity there is Insulcast with a conductivity of 0.46 W/mK @ 600C.

http://www.morganthermalceramics.com/sites/default/files/datasheets/1_insulcast.pdf

You may be able to mix them to dial in the conductivity you want.


May need to call them about food safety.

Offline shuboyje

  • Registered User
  • Posts: 1242
  • Location: Detroit
Now we are talking Bill.  I've never found a castable in that range locally, and the only supplier in the area could care less to help.  The first two have really peaked my interest.
-Jeff

Offline TXCraig1

  • Registered User
  • Posts: 16248
  • Location: Houston, TX
    • Craig's Neapolitan Garage
Why not the last? I think 0.3-0.4 W/mK is where you want to be for NP.
"We make great pizza, with sourdough when we can, commercial yeast when we must, but always great pizza."
Craig's Neapolitan Garage

Offline Hickory.Bill

  • Registered User
  • Posts: 10
  • Location: United States
  • I Love Pizza!
Why not the last? I think 0.3-0.4 W/mK is where you want to be for NP.

Likely the last one will be physically weak. 

As I eluded to in previous posts, only the last 1/2" or so need to be hard.   If you have 2" of 0.3-0.4 W/mK topped with 1/2" of harder 0.7 W/mK  you will not get heat transfer as if the whole mass was 0.7 W/mK.  There isn't enough heat capacity in the thin material to over cook the bottom.  Sure the 0.7 W/mK  layer will transfer the heat it has twice as fast as the thicker 0.4 W/mK layer, but once it's heat is gone, the heat will have to bleed up from the 0.4 W/mK layer at the slower rate.   Heat will also travel sideways through the 0.7 W/mK layer but as a practical matter it won't act like 2.5" of 0.7 W/mK castable.

Another idea would be to just get the calcined fire clay castable and split the batch when it's wet an mix in vermiculite or alumina bubbles with half and put that in the bottom of your form then top with the full strength.   Vermiculite is very cheap, but I'm not sure if there will be an initial burn off.  Alumina bubbles work great, but they are a bit pricey.  If you order alumina bubbles, make sure you know the volume, they are deceptive light.

Not sure where you guys are located, but you might try Southern Refractories in TX. TXCraig1 is from Texas.

http://www.southernrefractoriesinc.com/material-supply

Offline Tscarborough

  • Lifetime Member
  • Global Moderator
  • *
  • Posts: 3855
  • Location: Austin, TX
    • Pizza Anarchy
Insulcast has a fair amount of perlite aggregate, so it is not suitable for a flooring material.  I have some 12x12x2" pavers that are made in the same fashion and fired to the same temps as the Italian biscotti, but they are not composed of exactly the same materials.

Offline stonecutter

  • Registered User
  • Posts: 1004
  • Location: NY
    • Old World Stone & Garden
Why not the last? I think 0.3-0.4 W/mK is where you want to be for NP.
That's insulating firebrick range.
http://oldworldstoneandgarden.com/


When we build, let us think that we build for ever.
John Ruskin

Offline TXCraig1

  • Registered User
  • Posts: 16248
  • Location: Houston, TX
    • Craig's Neapolitan Garage
TXCraig1 is from Texas.

I'm lucky enough to have a biscotto floor.
"We make great pizza, with sourdough when we can, commercial yeast when we must, but always great pizza."
Craig's Neapolitan Garage

Offline shuboyje

  • Registered User
  • Posts: 1242
  • Location: Detroit
I wouldn't want to build a floor out of anything classified by the manufacturer as insulating and not dense.  That says it can be used as a hot face, but probably in the context of a hot face for walls in a gas oven.  A floor in a wood fired oven takes a beating comparatively.

I've cooked lots of Neapolitan pizzas on WG at 0.6 @ ambient temperature.  I'm sure they go up a bit as the temperature rises.  For my oven designs I'm pretty confident 0.69 @ 600C would be adequate. 
-Jeff