Furnace, Build 2 2024

Using the New Furnace at Winterfest Demo 2024

Last year I had a go at making a couple of furnaces. They worked well, and I learnt a lot, but there were a number of improvements needed. Last year's furnaces can be found here: Furnaces 2023 References can also be found at that link for the information mentioned here. 

My goal when making these was not to use modern materials in the construction of the furnace. I also wanted a furnace which could be worked by a single person. It also needed to be portable, so that I could bring it pre fired to an event without having to wait a week or longer at the event itself. 

I took it to Cold War 2023. The furnace met all these goals, though it broke when transporting home. I believe this was due to it getting wet at the event, and due to the composition used. The composition used was as follows; Slightly decomposed Horse Poo, Clay, Sand. I think I was too hasty and that the horse poo needed to decompose more. The idea is that the beadmaker would go and build their furnace near the river, using the materials there. The furnace would last a little while, but it was not a permanent build. The materials would have ample time to decompose though, so I decided to wait a year and try again with the same composition. 

I think it produced a material that was far more binding, as the fibres had split more and were able to blend and knit together far more effectively. However I am also certain it was a bit caustic, and would urge caution and the use of gloves in handling the blend. 

Much more broken down

More fibres

The original shape I used was modelled after the Ribe furnace. It was tall which allowed air flow to stoke the coals. I did not need a bellows to have the heat required to melt glass. The funnel allowed the heat to be centered at the top of the furnace which was a good point to melt glass, however I found that the best heat concentration was about 20 centimeters below the opening of the furnace. The shape of this furnace allowed me to use the survival fire method, which already primes the wood to have a good balance of air flow, producing high heat. It is not easy to move however, and whilst cracking is normal, the fault lines for this shape effectively cut it in half. You could fix this by making the walls twice as solid, but it would no longer be portable. 

Making the walls more solid

Building the shape up gradually

I spoke to Master Sui before building a new furnace, with similar goals to the first. He provided some insights into why and how it is possible to create a furnace without the use of bellows, and spoke about his experience and best results with certain shapes of furnaces. He also suggested not filling the chamber full of fuel, but rather have it half in to allow better air flow, and higher temps. 

I used this information, combined with last year's research to make a shape that was logical, likely to be used and effective. Amusingly, as I took the furnace to a demo for Winterfest 2024 , most folk called it a pizza oven, which it sort of does resemble. 

Annealling dishes on both sides

I also added rod rests, though rods were not as popular as tesserae in period. 

Due in part to the composition of the furnaces, there are not many extant examples. However we do see examples through history and recent history of low tech furnaces based on knowledge and ways passed down the generations. 

I used this to adapt my furnace slightly and add parts to anneal the beads. The process of allowing the glass to cool down slowly is important, and prevents the glass from shattering. There are a number of historical ways of doing this, having a clay pot near the fire being a common example. 

As I was working on the shape of this furnace, I decided to build in the annealing dishes to the top of the furnace. It worked very effectively, being hot enough to help transistion the glass slowly, but not too hot or too cold. 

The composition of the furnace, with waiting a year, and mixing the fibres a lot better, worked amazingly. I used river clay which I'm pretty sure made a difference as well. 

The furnace was portable. It fired up well. However, despite having the furnace going all day, I didn't get constant functioning heat at the tempertatures I needed. I think the fuel source had a small part to play in this, but I also think it was simply too small. 

Next time I will make it bigger, though I think it may no longer be portable at that stage. 

I will also try another idea, which is to place it on a built fire, and have it act as a funnel. I think this may be quite effective, especially in trying to achieve a pre made furnace, with the flexibility of being able to travel to events. 

Watch this space for that experiment. 

Annealing: https://mo-sci.com/glass-101-glass-annealing/ 

Annealing: https://www.sciencedirect.com/science/article/abs/pii/S0379073811000107 

Glassworking processes & properties [videorecording] / Corning Museum of Glass. Corning, N.Y.: Corning Museum of Glass, 2007. 1 videodisc ( min.) 

This educational video archive presents more than 40 short segments on the various techniques employed by glassworkers: including annealing. Commercially distributed.

Classes 2024

                             Classes with Contessa Ginevra Lucia Di Namoraza 

Rowany Newcomers: Introduction to Glass bead making

9/3/24 

Saturday 3-5 PM 

An introduction to glass beads through cultures and ages, including a practical section to make several of your own glass beads. 

Pre-booking required 

Please bring gardening gloves if you have them. 

Rowany Festival: Introduction to Glass bead making- Workshop 1 and 2

19/4/24

Friday 3-5 pm 

An introduction to glass beads through cultures and ages, including a practical section to make several of your own glass beads. 

Pre-booking required 

$10 fee for materials. 

Please bring gardening gloves if you have them. 

Coronation- Southron Gaard: Introduction to Glass bead making- Workshop 

5/5/24

Sunday 9-10 AM

An introduction to glass beads through cultures and ages, including a practical section to make several of your own glass beads. 

Visiting Mordenvale and Stormhold soon

Visiting Mordenvale and Stormhold soon. 

Private Tuition and sessions by arrangement.

Class Notes

https://gydahrafnsdottir.blogspot.com/2022/05/class-notes-2022-making-glass-beads.html

Researching and recreating Glass Beads through the ages 

An in-depth review and round table discussion of extant artifacts and advanced research and recreation techniques. This hour-long class will take participants through a variety of techniques and approaches to researching glass beads, recreating extant artifacts, creating your own interpretations, and providing detailed documentation. There will also be an overview of how to meet Lochac arts and sciences rubrics and using rubrics throughout the known world to improve your work and research. Books and other documentation will be available for participants to browse.

Historical Pink Glass

                                                        The 4th-century Lycurgus Cup, a 4th-century Roman glass cage cup made of a dichroic glass

I had a project to complete and the brief for the project was "Historical Glass Beads, "Valentine's Day" theme. My immediate thoughts were "pink" and "love hearts". Neither of these have much evidence across the pre 16th century world, so I decided on "red" and "white", and a couple of love heart shapes on the beads on the premise that feathering and odd shapes do ocasionally turn up. 

I thought I might collate any evidence of pink glass here. Any questions or additional sources, please feel free to add. 

Wikipedia: Cranberry Glass

https://en.wikipedia.org/wiki/Cranberry_glass 

The origins of cranberry glass making are unknown, but many historians believe a form of this glass was first made in the late Roman Empire. This is evidenced by the British Museum's collection Lycurgus Cup, a 4th-century Roman glass cage cup made of a dichroic glass, which shows a different colour depending on whether light is passing through it or reflecting from it; red (gold salts) when lit from behind and green (silver salts) when lit from in front.^[2][3] Kitab al-Asrar, an Arabic work attributed to Abu Bakr al-Razi contains one of the earliest modern descriptions of the preparation of gold ruby glass.^[4][5]

Rock Tumblers and Glass Beads

 

So for a while now, whilst studying extant museum glass pieces and recreating them, some things haven’t sat quite right.

The shape and the style can be recreated almost perfectly ( warts and all) but the historical glass look and feel is almost clay like. Almost to the point where sometimes it doesn’t look like glass at all.

This is generally explained by weathering and different glass composition and manufacturing tools and furnaces.

But knowing something and seeing it in action are two very different things.

My sibling got us a rock tumbler for Christmas. The tumbler mimics the ocean or natural wear and tear over centuries.

0.03 seconds after setting the tumbler on, I had to see what would happen if I stuck some glass beads in there.

So I grabbed a bunch of broken glass, and some random examples that I had previously made and popped them in there with the other rocks that were tumbling away.

Some of the glass ( mostly any of the clear glass) came out as gorgeous sea glass style. But the opaque glass and the Phoenician/ Chinese ones came out EXACTLY like the worn thousand year old clay like glass which was freaking cool to see. They’ve only been in there for 4 days or so, so I’ve chucked them back in to see how it continues to tumble. And it feels so smooth and rounded.

I was asked some interesting follow up questions. Tom asked if I thought the orginal beads were tumbled or equivalent in period or if this was just replicating the act of aging?

I answered with the following:

"I haven’t seen evidence to say it was done initially and on purpose, nor any equipment that says it would have been possible. Based on this I would hesitate to say they were tumbled on purpose.

I have seen evidence where some necklaces were found with hundreds of years of age variations on the one necklace, and wear and tear on beads in ways that suggested constant rubbing and deterioration over time caused by potentially one lifetime.

I would definitely say that this effectively replicates ageing over time based on the very similar look and feel, not only on a surface level but looking more carefully at the details of the deterioration of softer colours ( such as the white)"

Any other questions, please ask :) 

Building Medieval Furnaces

This post will contain a variety of information including the process of creating the furnaces, the materials and references used, the experience firing and using it , as well as information learnt through experimentation and discussing with others who have previously made these or something similar. I will continue to add to this post as I experiment. 

I have been very intrigued by the furnace from Ribe, particularly the recreations done by Thomas Risom. This particular furnace uses the materials found by a riverbed. They are accessible and evidence of the techniques used in this heat receptacle can be found across time and cultures. The other aspect that I am fascinated by is that the shape of this particular volcano furnace allows for high heats, and manipulation by one person, without the need for bellows or others to tend to the fire. It is also small and portable which means I can bring it to events to teach. Amazingly it is also much quieter than modern set ups!

Amusingly, I subsequently found that the experience of working with others was far more enjoyable in good company than doing it solo anyway.

Concepts discovered/Explored

-After 5 hours the coals and the furnace itself were hot enough to get the heat required. 

-Coals have been found in extant examples, rather than wood and that makes sense given the above information. 

-There are some commonly used structures that produce high heats. Can I combine these with the furnace, to help my heat management? I found out about Swedish fire logs and "Survival/Scout fires. Both of these simply use wood, positioned carefully to create strong air flow. At Festival, we used a small survival/scout fire in camp and out of curiosity I got my glass making tools out. The heat was enough to melt glass. So my theory is, if I build this style within the furnace, not only is it plausible that this would have occured, but it may be effective as well. 

-Swedish fire log: https://www.freshoffthegrid.com/swedish-fire-log/ 

-Scout fire: https://www.fieldandstream.com/articles/survival/fire/2011/01/build-bad-weather-fire/

Materials used:

-Slightly decomposed Horse Poo

-Clay

-Sand

-Hardened clay pot to be removed, instead of willow branch as the structure base. 

The Process:

   

Attempt One

This furnace produced a fair amount of heat. I used barely any fibers and sediment however, and the next day it promptly cracked. It was too thin, and had too much clay. 

Attempt Two

This furnace construction involved far more clay and sediment, including horse poo for fibers.This is when it was wet. I have placed it on a large cement tile that can be used to transport it.

Composition

A close up of the composition of the furnace. After discussions with Master Owen, it was clear that my original theory of adding more hay was not the way to go. More fibres was, and it looks much more solid now. 

Attempt Two

 

This is the furnace when it was dry. I drove this about 300 km for an event.With careful packaging it survived the drive and was used successfully to create a couple of beads. Unfortunately the winds were so strong that we made the decision to move it after we had fired it. Sadly, I had not been able to contain my patience during the week, and it hadn't really gone a proper week of drying and it didn't have enough fibres. As a result, it cracked when moved, the dry parts moving against the rest and falling apart. 

Melting Goodness

Lit up

End of Days for Furnace Two

Attempt Three

Attempt Three (and Four) involved crushing Attempt Two back down, and mixing far more fibres into the mix. I experimented with more diverse fibers that they would have had access to at the time, such as linen, wood dust and hay. As I was doing this, I ended up with a lot more materials than I had previously, so I decided to experiment with a smaller version. Firstly I was curious as to how much heat a smaller version could create, and secondly, I have seen extant examples where the volcano furnace had a carved rock as an extra layer at the top, or something that seemed like a second smaller furnace on top, and I want to see how that affects heat management if I place it on top.

Attempt Four

The mini version. I am curious to see if this might work, or not. It's small and has less air flow which makes me think it might crack, or not get hot enough. However it may also be quite effective on top of my furnace. 

Attempt Three

After three days of drying, adding sand externally and patting down to remove bubbles and less dense spots. It is drying well , even in the cold Canberra weather, and I hope to fire it up after a week or so. 

Attempt Three- Embellishments

After using a number of different furnaces, medieval and modern I have reached certain conclusions. One being, that if you did this over time and repeatedly, you would make changes to make your life nicer or easier. The indents I have added are places to rest my tools and glass. 

Ginevra/Gyda Glassmaking

This was one of my earlier attempts, which produced some beads. The heat was intense enough about 5 hours in. 

Ginevra/Gyda Glassmaking/Teaching

I didn't schedule any official classes at Cold War as I wanted to participate in War but also teach organically without a schedule. This worked amazingly in the Bjornhird Makers' Space, as people came in as we worked and asked questions or observed. After some safety briefings, a couple of very interested folk were able to make some beads over the furnace and take them home. I love sharing the joy of glass beadmaking. It's a lot harder than it looks, but the end result is super satisfying!

Using Master Owen/Sui's Furnace

This was very successful, particularly after the coals had been going for about 5 hours. 

This is a dirty hobby!

Some of the glass beads that were made

After the heat became workable, each bead became easier and easier. The consistency in the bead was on par with the use of modern methods, and adaptation to the particularities of the medieval flame was easy to grasp with some practice. 

Relevant Information:

"In its raw form, glass can be easily worked in a number of ways. Experimentally we have found that it can be directly worked into beads. Using a crucible such as those found at Paviken and Helgo

the raw material can be melted. By reaching into the crucible with a pair of tweezers and slowly drawing the tweezers back a rod of glass can be drawn from the liquid glass. Varying the speed of the draw will change the size of the rod produced. In the archaeological record this produces small lumps of glass with tweezer marks and small stubs of rods attached. These rods can be used to directly create beads in a style strongly related to modern lampworking techniques."

-Glass on Fire

"At Ribe, at least six hearths associated with bead production debris were uncovered.Hearth ÆZ is roughly oval at 53x23 cm. QA is a round lens shaped hearth approximately 50 cm in diameter. The remaining hearths are less well defined. UN is roughly rectangular. UR is irregular in outline.

Bencard et al define these hearths as being of a clay construction but the long section of hearth ÆZ

appears more consistent with a cob construction. Cob has been defined as “a material for walls, made from compressed earth, clay, or chalk reinforced with straw”

-Ribe Excavations

"They are generally rebuilt in the same place after completely demolishing the earlier ones. This results in an abundance of fired-clay fragments with glass spillage, clay pots, clay plates, arm rings, broken crucibles with a glass layer, and bricks and other debitage littered around the glassworks."

-Glass Beads in Ancient India

"Furnace designs changed over time but there were basically two types: tank furnaces and pot furnaces. Tank furnaces were built with an integral tank to contain the molten glass. There is some evidence for smaller tank furnaces being used in the Roman period in Britain to melt glass for shaping (Shepherd and Wardle 2009) and a number of good examples of tank furnaces used for glass making from the late 19th century"

-Archaeological Evidence for Glassworking

Volcano Furnace reconstruction from Risom 2013

Science Direct. Beadmakers in Egypt 

Fired Clay: Evidence of glass making furnaces. 

Image: © Amgueddfa Cymru - National Museum Wales

Furnace Links:

-Thomas Risom: The Bead Maker from Ribe

-https://historicengland.org.uk/images-books/publications/iha-glassworks/heag236-medieval-and-early-post-medieval-glassworks/

-https://www.academia.edu/15486278/Glass_on_Fire_Temperatures_in_reconstructed_Viking_Era_bead_furnaces_in_Can_These_Bones_Come_to_Life_Insights_from_Reconstruction_Reenactment_and_Re_creation_Vol_II

-https://www.cmog.org/article/about-medieval-glass

-https://www.researchgate.net/publication/354986153_BEAD_FURNACES_IN_ANGLO-SAXON_BRITAIN_An_investigation_into_the_likely_sources_of_heat_used_by_beadmakers_in_the_5th_to_7th_centuries_CE

-https://www.researchgate.net/publication/339178110_ANGLO-SAXON_GLASS_BEADMAKERS

-https://exarc.net/keywords/bead

-https://www.archaeology.org/news/10877-221005-ribe-bead-workshop

-https://www.sciencedirect.com/science/article/abs/pii/S2352409X20302790

- Mogens Bencard and Helge Brinch Madsen, Ribe Excavations 1970-1976 Volume 4 (Højbjerg: Jutland Archaeology Society, 1990)

-Heaser, Sue. (2022). BEAD FURNACES IN ANGLO-SAXON BRITAIN An investigation into the likely sources of heat used by beadmakers in the 5th to 7th centuries CE. 

-https://museum.wales/collections/online/object/8b8d8c64-392e-3d90-b4e7-ec28749a67c4/Early-Medieval-fired-clay-furnace-lining/?field0=string&value0=finds&field1=with_images&value1=on&page=4

-Glass Beads in Ancient India and Furnace- Wound Beads at Purdalpur: An Ethnoarchaeological Approach. https://core.ac.uk/download/pdf/5105475.pdf

-https://historicengland.org.uk/images-books/publications/glassworkingguidelines/heag259-archaeological-evidence-for-glassworking/