Late Anglo-Saxon Disk-Brooches. Part 6. (Enamelling Tools)

Goldsmithing and Enameling Tools: Iron Hoods / Muffles and Trays.

This is Part 6 of my series of blog posts related to my Late Anglo-Saxon Enamel Disk-Brooch project on the historical tools used in Goldsmithing and Enamelling from approximately the 2nd-century BCE until the middle of the 2nd-millennium CE.

Figures A to J.

I was inspired by the hood/muffle sets that two fellow Enamelers each fabricated and based on Theophilus' description from, 'On Diverse Arts'. A couple of years ago I saw the set made by THL Alys Treeby, my Apprentice Belt-Sister, she's had multiple successful enamel firings on a Blacksmith's charcoal heated forge. Recently Sir Ælfwyn Langanwuda sent me photographs of the set she fabricated. This past weekend she was able to use it with great success on her period bead kiln that she's repurposed, previously she used a blacksmith's forge as a heat source. Both of their hoods are appropriately 3-inches in diameter.

In May of this year, Doug Colin Guyton fabricated for me a perforated, domed hood/muffle and tray (see Figure M.) based on my research of Theophilus' Treatise, ‘On Diverse Arts’. Both the domed extant and reproduction pieces have handles though shaped differently. Theophilus' description is of a flat tray similar to a pizza paddle, and the domed Georgian extant tray is concave, similar to a frying pan.

Figures K and L.

Over the next year I plan to experiment with my muffle set using a charcoal forge to solder, enamel and fuse. I hope to fabricate another domed muffle/hood as well as conical shaped ones, based on the extant finds of the “Iron hood, Vani, second half of the 2nd century B.C.”.

The hood/muffle and its tray are used on a charcoal forge (see Figures B and O) or with a furnace, both are smaller than what Blacksmiths use(d). They are placed on top of heated charcoal and other heated pieces of charcoal are piled a couple of inches high around the hood. Since the holes in the hood/muffle were punched from the interior outwards, the sharp edges of the cut and stretched metal point outwards, much like a cheese grater, and help reduce how much ash and particles can enter. The charcoal quickly heats the metal and interior space. Once the needed temperature range and time have been reached then the charcoal can be carefully brushed away from the sides and the entire hood/muffle and tray can be removed from the forge or furnace. 

"A copy of the Colchian cloisonné hood was made and tested, which showed that the Colchian “hood" is a goldsmith's tool – an iron muffle. If placed underneath a pile of burning coals as described by Theophilus, high temperatures are achieved inside the muffle and a highly skilled jeweler can perform work on glass, gold or silver." (Ermile Maghradze, Nature, June 2014)

I am researching the writings of three other historical figures in hopes of finding more information on the tools and techniques of pre-Renaissance soldering, fusing, and enameling techniques. I will continue to write blog posts of my experiments and findings over the coming year.

Figures M to P.

Figure A. 

Ermile Maghradze fabricating a Gold Cloisonné enameled medallion based on an extant find. 

Figure B. 

One style of “Colchian hood” being used for Georgian style enameling on a charcoal forge. The one shown above is a reproduction based on an extant find (see Figure K and L). 

Figure C. 

Ermile Maghradze placing Gold cloisons on the back plate. 

Figure D. 

The perforated, domed hood looks like Theophilus’ description in his Treatise, ‘On Diverse Arts’, though this extant Georgian base is concave, similar to a frying pan, instead of flat like a pizza paddle, as in his description. 

Figures E & F. 

“Iron hood, Vani, second half of the 2nd century B.C.”, a conical style of perforated muffle / hood and its base, displayed in the Georgian National Museum. 

Figures G to J. 

A variety of Georgian Cloisonné enameled pieces.

Figure K.

The various tools used for fabricating Georgian enameled pieces, several are extant finds (both hoods), others are modern recreations based on finds and research. 

This conical hood is very similar to the “Iron hood, Vani, second half of the 2nd century B.C.” from page 57 of the article. 

The perforated, domed hood looks like Theophilus’ description in his Treatise, ‘On Diverse Arts’, though this Georgian base is concave, similar to a frying pan, instead of flat as in his description.

Figure L.

"One very important archaeological discovery in Western Georgia was a perforated, cone-shaped iron “hood” and a tray discovered in 1966 in the remains of a city near Vani in the historical region of Colchis. We made a link between this artifact and a type of “hood” used to mount enamel, which had been described by Theophilus. In the chapter of the treatise that explains firing gold plate with mounted enamel, Theophilus describes a “hood” with a tray that a smith has to use to complete the firing. It is apparently very important that Theophilus is describing one of the types of muffles (a clay or iron box inserted into a furnace in order to fire an article) that was widespread in the medieval goldsmith workshops."

- from, Ermile Maghradze (2014) 'The Discovery of the “Colchian hood”, a tool that shaped the art of Medieval Cloisonné Enamel Technology', Museum. Georgian National Museum, N1, June 2014, 54-57.

Figure M.

This perforated, domed hood was fabricated by Doug Colin Guyton based on my research of Theophilus’ description from his Treatise, ‘On Diverse Arts’. 

The base of the domed Georgian extant set is concave, similar to a frying pan, instead of flat like a pizza paddle, as the version that Theophilus was familiar with.

Figures O and P. 

The conical hood is similar to the “Iron hood, Vani, second half of the 2nd century B.C.” from page 57 of the article in Nature. Its base does not have a handle like the domed hood.

Figure P.

The perforated, domed hood looks like Theophilus’ description in his Treatise, ‘On Diverse Arts’, though this Georgian base is concave, similar to a frying pan, instead of flat as above in our Theophilus reproduction.

Figures A thru J, N, O, and several quotes are from: 

Ermile Maghradze (2014) 'The Discovery of the “Colchian hood”, a tool that shaped the art of Medieval Cloisonné Enamel Technology', Museum. Georgian National Museum, N1, June, 54-57.

Figure M.

Photograph by Gaeira Aggadottir.

Figures K, L, and P.  

These images are from the Georgian National Museum’s website.

Late Anglo-Saxon Disk-Brooches. Part 5 (Display 1)

Figure 1. Close up.

This is Part 5 of my series of blog posts related to my Late Anglo-Saxon Disk-Brooch research and fabrication Project. Part 1 is a general history of the disk-brooches that my research and fabrication project centers around.
On Sunday, August 4, 2019 I participated for the first time in the 22nd Annual Known World Arts & Sciences Display at Pennsic 48 with phase 1 of my Late Anglo-Saxon Enamel Brooch Project. From 1pm to 5pm I was one among a few dozen artisans displaying their projects from across the SCA Known World. 

The 9 glass bottles on the right half of the display are of my White Paste experiments which I'll be writing a blog post about in the near future. 

The colorfully filled glass bottles on the left half of the table are the enamels that I made from hand grinding several soft glass Lampworking rods of CoE 104 glass. [See Part 2, Part 3, and Part 4 of this blog series for more details.] The back row are the first 5 colors of glass rods that I ground. They were unfortunately contaminated from the marble mortar and pestle I used when I started this project. The front row of 6 enamels were entirely hand ground using a Stainless Steel mortar and pestle and fired beautifully as enamels. I switched to Stainless Stell once I read a passage from Cellini's Treatise in which he mentions using Steel, this made a great difference.

Figure 2. Full display.

It was far too windy to put out either the small Sterling Silver bezels I enameled, the glass beads I set with White Paste in bezel settings, and sample pieces of the glass rods. I will need to attach them to a sturdy backing before St. Eligius Arts & Sciences Competition in mid November, hosted by the Barony of Dragonship Haven, so they can be seen without risking their loss to wind or by getting tipped over.

These are 3 of the 4 currently printed out binders of my research sources. I've found other papers that I need to print out.

The two cutting chisels and Muffle set were made by Doug Colin Guyton. The overall muffle design is based on my research of both Theophilus and Cellini's Treatises. The muffle top is also very similar to one of the extant finds of Georgian enameling muffle covers in the Georgian National Museum.

Late Anglo-Saxon Disk-Brooches. Part 4 (Enamel)

Fig 1. Fired Hand-made Enamel Bezel Cups.

This is Part 4 of my series of blog posts related to my Late Anglo-Saxon Disk-Brooch Project. Please see Part 2 of my series for information on my reasons for experimenting with Flameworking glass rods and turning them into a fine powder which can be used as Vitreous Enamel. Part 3 covers my first series of experiments on breaking down the rod sections into smaller pieces and then grinding, rinsing, drying, sifting, and storing the fine glass particles of each color of glass. Part 1 is a general history of the disk-brooches that my research and fabrication project centers around.


A few lessons learned:

It's impressive the huge difference various tools can make when compared to one another. 


Contamination from the Marble Mortar and Pestle caused Light flecks 

My hand-ground Enamel was also contaminated with white and clear particles (Fig 1, 4, and 5). The significant differences can be seen between the bottom most red enameled bezel cup (Fig 1), which was ground only using the Stainless Steel mortar and pestle (Fig 2), and ALL of the other samples, which were ground mainly with the Stone mortar and pestle (Fig 3), which is possibly made of Marble, before switching to the Stainless Steel set (Fig 2). 

Fig 2.  Stainless Steel mortar and pestle

It turned out that the Stone's hardness wasn't as high as we thought compared to that of the glass being used. Unfortunately, I wasn't able to find, when I searched online using Google, what the range of hardness was for CoE 104 (Coefficient of Expansion) Lampworking 'soft' glass rods. Looking at the "Mohs Scale of Hardness", ". . . glass rates about 5.5, and a steel needle is a 6.5. Most Granites rate about a 7 in the scale while most marbles, limestones, travertines rate in the 3 area." [Source; accessed 2June2019], "Stainless Steel 5.5-6.3" and "Soda (soft) Glass 4.5, Glass 4.8-6.6" [Source; accessed 2June2019].

Switching to using a Stainless Steel mortar and pestle (Fig 2) made a significant improvement, both in the speed and ease of breaking and finely grinding the Flameworking glass rods into 80-mesh Vitreous Enamel. 

Fig 3.  Stone mortar and pestle.

Theophilus, in his treatise, "On Diverse Arts", doesn't specify which materials to use for either the mortar or pestle. This is most likely due to him expecting his contemporary reader to know and own the appropriate one(s). 

Benvenuto Cellini advises in "The Treatise of Benvenuto Cellini on Goldsmithing and Sculpture", "a little round mortar of well-hardened steel, and about the size of your palm...with a little steel pestle specially made for the purpose of the necessary size." (Fig 2)

I had started to grinding all of my Flameworking Glass rods with the Stone mortar and pestle (Fig 3) which looks like white 'marble' with pale grey veins. I found that grinding the CoE 104 Flameworking glass was quickly causing wear and tear to the mortar, but especially to the bottom concave curve of the pestle. 

Switching to only using a Stainless Steel mortar and pestle (Fig 2) made a significant improvement by eliminating additional contamination from the Stone mortar and pestle's surfaces (Fig 3).

Unfortunately, rinsing out the ground up glass multiple times did not remove the contamination, it stayed and caused, at a minimum, color issues and a great deal of very fine white speckles throughout all the colors, as can be seen in the photograph (Fig 1). I do not know what possible chemical interactions could have occurred during the firing that reached 1,500F.

Fig 4. Rows #1 & #4 are Stoned,
The photos are at two different angles.

I started to stone the highest surface with 150 and 220-grit Alundum Stones so that the glass and metal would be uniformly level (Fig 4. Rows #1 & #4 are Stoned in all 5-colors). Quickly it was obvious that additional enamel layers needed to be added so that the center of the concave glass, concave meniscus (Fig 4), could be filled in and raise closer to being level with the bezel cup's walls. This would help reduce how much metal and glass would need to be stoned away to complete the stoning stage.

Once I've added sufficient layers of enamel I will need to finish: stoning, pickling (pickle is a mild acid solution that removes oxides from the oxidized Sterling Silver), flash fire (to make the glass shiny once more), and polish the Sterling Silver bezel cups to complete the process.


The importance of using the correct temperatures

Fig 5. Melted Bezel Cups

The hand-ground Lampworking (soft) glass that I made in five Anglo-Saxon colors, which has a CoE 104, was sifted so that it is the standard 80-mesh size that Thompson Enamels sells. This hand-made enamel was wet packed in multiple thin layers within the Sterling Silver Bezel cups and fired each time an additional layer was added. The Bezels melted in the Kiln when it reached approximately 1,700F, it is usually set to 1,500F (Fig 5). 

If Copper and either Fine Silver (99.999% Cu) or Sterling Silver (92.5% Ag and 7.5% Cu) are physically touching one another when they reach their melting points then the Silver will look like it is melting into the Copper or look like it is being absorbed by the Copper. The Silver (Ag) atoms slide within Copper's (Cu) crystal lattice. Silver and Copper are Eutectic [also called, Eutectic System].

This can be prevented if there is a layer of glass / vitreous enamel between the Copper and Silver, *Enamelers call it 'Flux'. As soon as the glass is thinned away over several firings and leaves a bare spot, during the needed temperature range, then the Silver atoms "slide" into the Copper (Cu) crystal lattice. 


* 'Flux' in Enameling is clear glass enamel, but it should NOT be confused with what Metalsmiths are referring to as Flux, which can be made in different ways, but usually it's a solution of Borax mixed with water. Flux (Borax, etc.) helps prevent oxides on hot metals from forming, molten metals flow better, the solder binds to the metals and flow more easily.


Silver and Copper has are Eutectic [also called, Eutectic System], both elements are Face-Centered Cubic (FCC) structures (scroll down to see a 3D image of the structure; "The face-centered cubic (fcc) has a coordination number of 12 and contains 4 atoms per unit cell." Source; or for a digital animation.)

Cu/Ag Eutectic System, "Copper and Silver are both FCC, but their lattice parameters and atomic radii are very different, so they have limited solubility in the solid state. There are two solid stable phases α and β, and at high temperatures there is a eutectic reaction where the solids α, β and the liquid coexist.", "Cu – Ag System, Cu: α phase, Ag: β phase", "Eutectic means “easily melted” in Greek." [Source; see slides 1-4]


Contamination from the Copper sheet causing Dark flecks

Fig 6. Flaked off Oxides from the Copper sheet that was
used as a support for the bezel cups during the kiln firing.

The dark flecks in the fired Enamel Bezel cups are from the flaking off of oxidized layers that were formed on the Copper sheet during the high temperatures reached within the kiln. 

I used the Copper sheet within the kiln to support the small Bezel cups during the firings. The metal mesh screen that is usually used on it's own to support Enamel pieces didn't properly support the Bezel cups so that they could remain flat (on the Left of Fig 5; Fig 6). The flaking black oxide layer can be seen underneath both the melted and whole bezel cups (Fig 5) and in the pile accumulated after the firings (on the Left of Fig 6). 


My Video of the Enameled pieces being removed from the kiln and cooling (on Facebook)

My short video is 3m25s long and shows a kiln firing of the hand-ground enamel I've been making from Flameworking glass rods.

The target kiln temperature is 1,500F for my enamels. At the start of the video the temperature is 1,450F (it might sound like I said 450F, but it's 1,450F) I open the kiln door to allow some of the built up hot air to vent out and get the kiln down to 1,250F. Once it's reached 1,250F (not 250F as it might sound like in the video) I gently place the Stainless Steel sheet, that's resting on the steel mesh frame, onto the kiln floor and close the door.

As soon as the temperature reaches 1,500F I carefully open the door and remove the sheet and metal frame with a pair of long pliers and place them gently on top of a ceramic tile. At the same time I'm wearing one heat protection glove on my dominate right hand that's holding the pliers, the heat is so high that even 5 to 10 seconds of exposure on my skin starts to sting.

The pieces change colors as they cool down from 1,500F. Once they are completely cooled they can be moved and worked on.


Part 5 of my series of blog posts will be about the results of firing the newest batch of Enamels that I've I made using just the Stainless Steel mortar and pestle. Once again I will not be mixing my Enamel with my Thompson Enamel powders due to the different CoE which could cause issues.

Late Anglo-Saxon Disk-Brooches. Part 3 (Enamel)

Fig 1.The first four colors of Flameworking glass rods that I
processed into fine powder to use as vitreous enamel.
Next to each plastic container is a piece of the
glass rods that I used as a source for the glass.

This is Part 3 of my series of blog posts about my Late Anglo-Saxon Disk-Brooch Project. Please see Part 2 of my blog post series for information on my reasons for experimenting with Flameworking glass rods and turning them into a fine powder which can be used as Enamel.

Part 1 is a general history of the disk-brooches that my research and fabrication project centers around.

At the start I used Propane fuel with a standard plumbing torch head to heat up the glass rods (Fig 2). My sheet of Stainless Steel was on top of the table with the mortar on one end next to the sheet. 

Fig 2. Left over fragments from
3 Flameworking glass rods.

The mortar was filled with ice water, this is where the heated glass will fall and shatter due to the thermo shock (Fig 3 & 4). The temperature change between being heated up and the ice water will over stress the glass and cause it to break into tiny shards due to the sudden cooling effect. The ice water also containing the pieces within the water and prevents them from flying about.

Fig 3. Once I switched from using Benzomatic's
Propane fuel and a basic torch head
their MAP-Pro and Hot Head torch .

I started with the red opaque glass rods. I held a length about 2 to 2 1/2 inches in a pair of long handled pliers and heated up as much exposed glass without getting the pliers in the flame. I didn't reach molten temperatures before I dropped the full length of rod into the cold water. It shattered a bit, but not as much as I had hoped. I continued with this method until I had enough shattered pieces in my mortar.

Fig 4. A close up.

I moved on to the next series of steps, crushing and grinding. I spent 10 to 30 minutes crushing and grinding the pieces with the pestle against the inner curve of the mortar. Every time that the water becomes very cloudy I rinse away the 'fine' or 'fines', very fine particles that float and cloud up the enamel's look, and added fresh water before grinding some more (Fig 5). 

Fig 5. The tilted mortar exposes the hidden
ground particles. More grinding is needed.

After the final rinse  (Fig 6) I spread the paste onto heavy duty aluminum foil for them to dry in the toaster oven, set at a low heat (Fig 7). Once cool I placed the contents of the mortar in a plastic 40-Mesh Enamel sifter and sifted it into a small bowl with the aid of a brush to move the particles around. When it stopped separating (Fig 8) I poured the fine particles, that the sifter removed, into a plastic storage container with a tight fitted lid. This is ready to be used as Vitreous Enamel.

Fig 6. Ground and rinsed a few 
times, this is ready to dry.

I placed the particles that stayed in the strainer back into the mortar, added some water and continue grinding, rinsing, drying, sifting until I was satisfied with how much I was able to grind fine enough for enameling. Then I moved to the next color and so on.

Fig 7. The paste is spread onto heavy
duty aluminum foil, dried in a
toaster oven at a low heat until dry.

Once I switched to the blue glass I decided to try heating the glass rods with MAP-Pro and switched to the Hot Head torch head, this heat source gave better results. 

At the same time I stopped trying to heat as much of the rod as I could in one go and decided to bring the last inch of glass to a molten stage and create a large drop shape. I continuously rotated each glass rod while heating it until it became molten. By slowly twisting and turning the rod in the flame I created a large teardrop shape which shattered in the ice water once it detaches from the rod. 

Fig 8. Sieving the dried glass through a 40-mesh
screening. The particles in the mortar are
smaller than the ones that are still in the sieve.

The extreme temperature difference between being molten and then hitting the ice water, with the added ice cubes, caused a greater thermo shock with more breakage. Success!

Once I have enough length of the glass rod shattered I remove the ice and some of the ice water. I continued with the above method of grinding, rinsing, drying, sifting, storing particles for all my lengths of glass.

Fig 9. Top row: Particles smaller than 40-mesh.
Bottom row: Particles larger than 40-mesh.
Left: Opaque red glass.
Right: Translucent dark blue glass.

Due to time constraints and the wear & tear on my hands and shoulders I spent 2 1/2 days processing the glass rods into 80-mesh enamel particles. With that in mind I didn't completely crush all of the glass that fine, I kept some larger particles for future comparison and to also work on some of it in the future when time permits. 

The Sterling Silver Bezel cups that I have are about the size of the ones on the brooches lobes and I have more than enough ground enamel for test samples as well for making one brooch for display.


Suggested Tools and Supplies

• Flameworking glass rods in several colors all in the same Coefficient of Expansion (CoE), these are usually used to make glass beads. I used CoE 104 Opaque glass rods.
• Benzomatic's Propane fuel, it burns at 3,600 degrees Fahrenheit.
• A standard plumbing torch head
• Benzomatic's MAP-Pro fuel, it burns at 3,730 degrees Fahrenheit
• A Hot Head torch head.
• A lighter.
• Safety Glasses
• A pair of long handled Pliers or glass rod holder.
• A none burning work surface like a large cookie baking sheet, piece of Stainless Steel, etc. (as seen in Fig 3)
• Granite or Agate Mortar and Pestle set (as seen in Fig 3 & 8).
• Ice and cold water.
• A 'Plastic 40-Mesh Enamel Sifter with Handle'. Item # 119305 at RioGrande.com (as seen in Fig 8)
• Several small bowls or white paper, Fluted Baking Cup for cupcake/muffins. To temporarily store dry, crushed glass.
• Aluminum foil or Aluminum pie plates.
• A funnel or a sheet of paper folded into a funnel.
• A paint brush for Art oil painting or a soft 'dollar store' paint kit brush. An old toothbrush would work as well.
• Several small, plastic storage containers with lids or old pill bottles that have been cleaned and dried (as seen in Fig 9).

Please NOTE: A 14.1 oz tank of MAP-Pro fuel is about 3 to 4 times the cost of a 14.1 oz tank of Propane, but MAP-Pro gas will heat the glass faster and to a higher temperature than Propane especially with the different torch head which is designed for Flameworking, melting glass. If you do not already have a 'Hot Head' torch head or a similar Flameworking torch head then use a plumbing set of tank and torch. It will take a bit longer to heat up the glass. An oven does not reach the needed temperatures to melt glass.


Part 4 of my series of blog posts will be about the results of firing the Enamels I made. I will not be mixing my Enamel with my Thompson Enamel powders due to the different CoE which could cause issues.

Late Anglo-Saxon Disk-Brooches. Part 2 (Enamel)

This is Part 2 of my series of blog posts about my Late Anglo-Saxon Disk-Brooch Project. In this part of the series I talk about my reasons for experimenting with Flameworking glass rods and turning them into a fine powder which can be used as Enamel.


Part 1 is a general history of the disk-brooches that my research and fabrication project centers around.

I purchased several end bits of Lampworking glass rods, which are used in bead making, in several of the colors used in Anglo-Saxon glass beads, in order to make my own vitreous enamel. Full, new rods aren't necessary since I will be crushing them. I also like the idea of recycling in this way, something I'm certain was done in period.

I only needed the end bits since I will using the technique discussed by Theophilus in, "On Divers Arts" to make my own vitreous enamel. Using thermal shock I will shatter them into smaller pieces, then crush them with a pestle with some distilled water, to reduce the dust in the air and as a bit of a lubrication, until they are finely ground. I will be wearing a good quality 3M respirator for fine particles and eye protection.

The bottom, horizontal rod is Marshmallow white which is the only full rod that I purchased that day. I have a couple dozen rods I purchased at previous EK Metalsmiths' Symposiums for making Viking Age beads, some of those rods might be the needed colors.

The dark looking rods between the white and turquoise, as well in the second picture, is actually a transparent, dark blue which is lovely.

I've been researching the sources for Anglo-Saxons enamel and so far it seems to be the same glass used for Anglo-Saxon beads. I will be writing a separate Blog entry about this section of my research.

I will also be using Thompson's lead-free enamels on several of the Anglo-Saxon brooches, though I will not mix these  on the same piece with the enamel I will make. The glass rods have a CoE* of 104 and the Thompson lead-free enamels have different CoEs depending on which series they are from.

* CoE = "Coeffecient of Expansion"

Many thanks to the discussion and helpful information from Mistress Elysabeth Underhill, O.L. during EK Metalsmiths' Symposium 17 (MSS) this month. She was generous with her time to help pull out these color rods from a large container of them to aid me in my project. I greatly appreciate it.


Links:
Late Anglo-Saxon Disk-Brooches, Part 1

My Facebook Photo Album of this project