Why and How Glass Breaks

I spent far too much time last week contemplating why we apply pressure on the opposite side of a score to break glass, and had to do a few more ‘GLASS IS NOT A LIQUID’ screeds. I decided this was worth a blog post. THE SCIENCE OF WHY AND HOW GLASS BREAKS.

1 - What Glass Is!

Please, repeat after me, GLASS (clap emoji) IS NOT (clap emoji) A LIQUID (clap emoji)! In grade school we learned that there are three (or four) phases of matter, right? Bad news, Mrs. Thompson lied to you. Ok, didn’t lie, just grossly oversimplified. 4th graders probably won’t understand the degradation of neutrons.

Solid – A uniform and dense configuration of tightly-bound molecules gives us rock, wood, ham sandwich, our skulls, etc.

Liquid – Less tightly bound and it’ll slosh around in your whiskey glass

Gas – Freer still, and it’ll fill up a room or otherwise expand to fill a container.

You might have also gotten to Plasma, which is the bright flash of lightning during a storm that ruins your day if it hits you.

Glass doesn’t fit neatly into any of these, so over the years various stories have developed. It must be a liquid, it must be a solid, etc. The truth is there are a lot more than 3 or 4 phases of matter, and glass is in a category of its own. It’s an ‘amorphous solid’ but that puts it in its own category along with degraded neutrons and other more unique things.

1b – Glass is NOT A LIQUID, pt 2.

The amount of time it would take for a glass object to ‘melt’ is something like ‘the age of the universe’. There is a very common misconception that old window glass is thicker on the bottom because it has flowed that way. If that were true, we wouldn’t have glass objects from Ancient Egypt and Rome. People wouldn’t have heirloom glasses older than grandma’s house with the weird windows.

The reason there is a thicker part to the window is that older methods of making glass sheets (e.g. the crown and cylinder methods) produced a sheet of irregular thickness. It’s some kind of ‘common sense’ to put the thicker part down for stability, but it’s not a rule and contrary examples exist.

1c – Wait, you didn’t really explain what glass is

Glass is solid, in the common sense that it’s not a liquid, gas, or plasma at room temperature (on earth, etc etc). But its structure is very disorganized, which is why it has similarities to a liquid. If its molecules were more orderly you would have "devitrified glass" ("de-glassed glass"), which qualifies as a ceramic.

Because of that attribute, a sheet of glass has strains within in. Various internal pulls and pushes and twists, so to speak. When glass is annealed a great deal of the stresses are able to resolve themselves, but not all. This is also why glass doesn’t have a grain like wood.

[Update: I thought it might be good to note that while current science identifies glass as a separate phase of matter, earlier academic documents would refer to it as an "amorphous solid" and, going earlier still, as a liquid. I believe that was accurate (for the time) using a very scientific definition of liquid as opposed to the common understanding. However, "Glass is NOT a liquid!" is much more concise than "Glass does NOT melt into new shapes over the course of one or two hundred years because it is not a liquid in the layperson's meaning of the term which has been superseded anyway by scientific progress and the inexorable march of time!"]

2 – How glass breaks, unsupervised

As is usually the case, force likes to take the Path of Least Resistance through glass. If a substance has a grain, like wood, you may be able to guess how it would split if hit with a general force. But in the case of glass, there is no grain and the stresses are mostly invisible[0]. As a result if you hit a piece of glass the fracture lines will follow the path of least resistance taking advantage of these faults and weaknesses until it reaches the edge of the sheet.

It's interesting to note that research (source below) shows you can apply less force than is needed to run a score if you apply it for a longer amount of time, even as much as 50% less. The authors note that if glass is under strain, it REALLY needs to be protected or minor damage may destroy it.

3 – How glass breaks, supervised

All we are doing when we break a piece of glass is coaxing the path of least resistance to be a route we want. I’d say ‘choose’ but if you’ve spent more than five minutes breaking glass you know it’s more of a coaxing and/or tearful pleading.

A typical modern glass cutter has either a steel (cheap) or tungsten carbide (much better) wheel that is shaped like a chisel. Incidentally the angle of that ‘chisel’ MAY have an influence on the cutting. I had never ever heard of this before until someone mentioned it (from a Wikipedia article). That article refers to a book on automotive glass and says a more sharply angled wheel cuts thicker glass better, from 120° - 154°. I don't work with industrial glasses so maybe that is common knowledge to them, but 154° is oddly specific to me.

Bob Beranek; Ann Schuelke (1 August 2011). The Complete Guide to Auto Glass Installation. AuthorHouse. p. 336.

Both steel and tungsten carbide are harder than glass, and so they are able to bite into the surface of a sheet. Carbide is just much harder than steel, so it is more durable. Usually steel wheels are found on cheap cutters you get at a hardware store. Carbide wheels are what you would expect from a specialty store and most anything directed at the stained glass market. Carbide cutting wheels also almost always have an oil reservoir in the handle.

Why oil? Its more to do with the tool than the glass. The stress of scoring glass builds up heat, which could eventually mess with the tempering of the metal wheel. It won’t generally be enough to cause thermal shock in the glass, but little glass particles are also caught in the deposited oil and that’s a good thing.

Fun fact, researchers (source below) discovered that the pressure applied to your cutter has an S-shaped effect on the force required to run the score (that is, break the glass). Once you reach the minimum force needed, adding pressure (pushing down your cutter harder) actually increases the torque needed to break it... until you blow past that zone in which case more pressure makes it easier again.

3b – Bringing it together

When we ‘cut’ glass we are actually introducing a known fault line into the glass in the hope and expectation that, when flexed, the path of least resistance will follow our score. And we all know that, sometimes, it doesn’t. Maybe a curve was too sharp and the PoLR was a straight line. Maybe a seed (bubble) was present that coaxed the line askew at a point, and then the PoLR is to follow the new angle instead of bending back to the score. Those invisible stresses can also be at fault, because glass is a temperamental mistress and lives off our tears. Wait, what? </Bitter Glazer>

4 – So, why DO we press from the opposite side of the cut.

It bothered me that it made sense in my mind, but I couldn’t explain it in words. I actively chewed on this for the better part of a week, thinking in terms like a race track. If you’ve seen one, you probably noticed that the starting line is staggered, and the closer to the center you are the further back you begin. This is because the center ring is smaller, and shorter, than the outer rings so that racer has to be further back to get the same distance. I was trying to leverage that rationale to explain breaking a flat sheet of glass and it didn’t quite work until I stopped thinking about a donut-shape.

 Not my best drawing, but showing that running pliers (or your thumbs) applying pressure on the cut effectively applies pressure to squeeze the score line. You might get the glass to break but it will be uncontrolled and unguided and probably isn't following your score. Note that the score is magnified A LOT in this drawing.

Another little sketch showing a greatly magnified score under no pressure, some sort of light pressure, and finally breaking pressure.

Incidentally this CMoG blog post has an even better graphic of this I found two days later, using foam.

5 – Bonus: Why your hand position is so important when cutting

I originally learned to cut glass by holding my cutter like a pencil. It's not quite that relaxed or the wheel wouldn't be able to contact the glass, but similar. I also noticed my accuracy was never where I wanted it to be, and I was always grinding pieces, finding new ways they didn't fit my pattern, grinding other areas of the piece, and eventually throwing it into scrap. After I began teaching with Molly I learned from her the "peace sign" grip that is pretty universally called for in professional-grade books.

  

My hand holding my favorite  cutter in a comically relaxed pencil grip, a much more likely pencil grip, and finally a 'peace sign' grip. The camera was not straight on, but you can still clearly see how the first two are further off-center than the last.

 I haven't found solid research into this, but I strongly believe that when you hold your cutter off-center, the score itself (and the associated "microfractures" if you believe that idea) are also at an angle. Least resistance being what it is, I suspect it would be more like a J-shaped curve than an actual diagonal, but you end up with a cut that is not perpendicular to the surface of the glass, what I know as a shelf [1]. Shelves are ridiculously sharp and seem to disappear if you even bring them near a grinder. I think that this is why my accuracy was poor for a long time;

You can see the 'shelf' on this piece, right above the little bump. It took me seven tries to hold a cutter wrong and get this piece

Holding the cutter off-center isn't going to give you a shelf every single time, or I would never have lasted this long in the hobby, but for me there was a major reduction in shelves and an increase in accuracy when I learned to use the better grip. Shelves are ridiculously sharp and will cut through your copper foil and your fingers effortlessly, not to mention (again) mess with the size of your piece. Probably a half-dozen times I have cut myself on a shelf-y piece and watched the delay as my skin realizes it's been cut, recovers from its shock for a second, and THEN starts bleeding. 

Allegedly neurosurgeons use obsidian scalpels because glass can be 100x sharper than steel. I believe it can be sharper than steel but about a year ago when I tried to investigate this, it seemed these scalpels were only an experiment.

6 - Really Cool Bonus: Glass Heals

I had heard Molly talk about this fact one summer while we were teaching. I'll be honest, I didn't believe it. How can a glass score heal and become more difficult to run if you let it sit for a few days? While doing other research, however, I found an academic paper from 1937 (Info below) that tested and proved the concept.

Their research showed that if you scored glass and let it sit, the amount of force needed to run that score increases over time, maxing out around 16 days. By the third day it's done the vast majority of its 'healing', however. Their hypothesis is that over the course of days the innate stresses in the glass will work themselves out a bit and reduce the effectiveness of your work. 

In conclusion, glass has a number of odd behaviors that bring to mind the expression "wibbly wobbly timey wimey", we work with the glass and beg it to do what we want, and windows aren't melting because GLASS IS NOT A LIQUID.

--------------------


[0] - There are polarized filters you can look through that will show the strains, but I don't THINK they are practical for non-scientists and I'm pretty sure they aren't the same thing that lets you tell which side of float glass hit the tin.

[1] - I am finally reaching that age where I can't quite remember whether I came up with this term myself or if I learned it from Norma/Danielle at GlassLink a decade+ ago.


Sources:

https://www.scientificamerican.com/article/fact-fiction-glass-liquid/

https://www.scientificamerican.com/article/is-glass-really-a-liquid/

https://en.wikipedia.org/wiki/Phase_(matter)

https://en.wikipedia.org/wiki/State_of_matter#Glass

https://io9.gizmodo.com/the-glass-is-a-liquid-myth-has-finally-been-destroyed-496190894

http://users.monash.edu.au/~ralphk/glass-cutting.html
(I'm not fully convinced on several concepts Mr. Klimek writes about, such as using spit to help run a score or the idea of microfractures, and we now know that glass is not a liquid but the anecdotal information is entertaining.)

"Concerning the Cutting of Glass" by MERTON W. JONES AND JULIAN M. BLAIR
Journal of Applied Physics 8, 627 (1937); https://doi.org/10.1063/1.1710352

https://blog.cmog.org/2015/06/03/part-2-why-does-glass-break/

Estelle's Vigil: Scarab Platter

EDIT: I've had to do something stupid to get the text to appear on this post. Sorry!

Estelle has, as one of her personal badges, a scarab (dung beetle) pushing a ball of it's preferred element. It's a reference to her peerage theory, quoted here:

The Dung Beetle Theory of becoming a Peer:

First, you gotta find your shit.

Roll around in that shit a while, make sure it's the shit you want to bring home.

Then, you get your shit together.

You gather it up, make it nice and rounded, polish that shit up so that it shines.

Then, you gotta bring your shit home.

So you spend your time, rolling that shit along.  But because you're a dung beetle, you gotta roll it backwards, which means that you really have no clue where you're really headed... but eventually, after a long while, and with a little luck, you get that shit right where it needs to be.

And that's how you become a Peer.

The End.

She requested a scarab platter on which she can serve truffles during her vigil. She provided a design:

We went through available molds and glass colors to find something acceptable:

(There is an invisible piece of clear for the white in this picture. The glass looks slightly hazy -- to me it's as if someone spilled milk on it and wiped most of it off. It was sold as "cloud" and as a translucent white. It wasn't translucent as I would find out...)

I was a bit concerned about how to fire this one. Before I started this piece I had fired one half of the family badge plate (adjacent post). I think it's issues were closely tied to the irregular layering of the glass (2 layers in some places, 1 layer in others). I added more clear pieces to this blank (what I call the piece as it's being fused, before slumping) to try and keep more consistency.

The piece is not perfectly regular, which didn't surprise me. A little grinding fixed that up. There are some unfortunate lines between the body segments, and leg segments. I knew that would happen but I didn't want to overlap the pieces and potentially provoke bubbles. This picture shows how the white striked. I compared it to a piece of "opaque" fusible white, and the piece sold as opaque was actually more translucent than this cloud glass.

With these platters I progressively slid my firing schedule down from 1300 degrees. I think its near 1230 now, with no change in the hold times. I did that to try and avert "dog boning" especially in the square plates. This helpful advice came from the folks at Fused Glass Fanatics on Facebook.

These pictures show the completed (slumped) platter. The actual shape and depth is not conveyed well, I will try to take a better shot next week. The white is clearly NOT translucent. I used my grinder along the edges to make the shape a little more regular and remove some stabby-bits.

Estelle's vigil: Family Badge Platter

Estelle did not ask for this, but some time ago we discussed the idea of making a matched set of platters that, when joined, would form her family badged (used by her whole mundane household). I decided this was as good a time as any!

The plates feature blue bars on a clear (white) field, with green in the corners (skipping heraldry terminology for non-heralds). Because I use a base layer of clear, I didn't see the need to fill in the second layer with clear. This is the first time I've tried any fused project with clear. I expected that the blue might spread or contract a bit, but I thought it would be acceptable:

HUGE bubble. Right beneath the base layer, not between two. The edge was also very irregular. ALSO, the grey sharpie used to tag the glass didn't burn off as I had expected. So, scrapped it and started over.

This time, I added clear layers in the top. The results fused much more smoothly:

And the slumping went well. Initially the shape bothered me, I thought I was seeing the "dogboning" problem I've had in the past with this mold, and I had been correcting my slumping temperature down to try and adjust. After a couple of days I realized they are fine; the molds have a slight curve in a plane I didn't realize, and the shape is closer to the mold's shape than I thought.

The piece in the top of these pictures had some old kiln wash fuse to the glass. For the immediate purposes, this is fine, but I plan to remake it so it has the clarity of the second (bottom) tray.

Lessons Learned:

• Applied kiln wash apparently has a shelf-life!
• Better results with even layer coverage.

Laurel Scroll of Dame Estelle de la Mer

Long, long ago a dear friend said "If I ever get elevated, I want you to do my scroll." It was a tremendous honor, considering she is one of the best scroll makers alive. Suddenly a few months ago Baronessa Estelle de la Mer was put on vigil and it took two days for the panic-screams to abate.

For the design, Estelle said she wanted something fairly simple, her device and a laurel wreath. No calligraphy (she wanted to make it painless on the scribe). She found a wreath she particularly liked (the border in the below picture) and I started working on understanding the shading of the pieces:

For the border I chose a green glass that looks like healthy vegetation. I think of it as a "living green"

I ran into one snag at this point. The pattern I had cobbled together had a somewhat indistinct cutline, and I tried to make it work. I do this too often, and I know it's a terrible idea. I then spent hours trying to grind all five pieces into complacency, and the results were terrible. The gaps were large, irregular. As minor as it seems, I was pleased that I eventually realized the right course was to transfer a clear cutline to new paper and scrap the first five. I was unhappy at having to scrap a square foot of clear, but I would have been infinitely unhappier to give my friend crap work for her elevation to the Laurel. The above picture is the recut pieces.

For the center roundel featuring her device, I could only come up with a few ways to do it. The first and obvious way is just piecing it together. Because her device has a complex line of division (a chief engrailed) and a charge over a line of division (a mullet of nine points) I thought the lead lines would be too much. Discussing it with Molly here at Pennsic, she suggests that it would have been fine, and that the mind would ignore the lead lines altogether (particularly if they were not straight "industrial" lines, a tip she received from my Laurel). I'm going to sketch out a few ideas for paint-less designs and see how I feel about them.

Another alternative (suggested by Kirsten, my laurel) would have been to use flashed glass for one of the two colors, and enamel in the other one. With the terrible lesson I got about this green enamel (See below), I would definitely use green flashed glass and put in the blue with enamel if I had to recreate this piece today.

My past experience with Reusche enamels has been hit or miss. The first time I used the sapphire blue enamel the results were amazing. I've previously done Estelle's albatross badge with it, and they worked flawlessly. The greens I've tried (two different ones) did not give me the results I desired at all. I did some research and found Fuse Master enamels that claimed to have almost the transparency of stained glass sheet and their sample pictures showed the vibrant colors I wanted. I ordered two and did some test pieces:

When I do a test chip for a new paint, I try it spread thin, and applied thickly to try and get a feel for the range of possibilities. They do turn out quite transparent; I couldn't get a pleasing picture of the heavy green test with my phone camera, but held up to the light it was comparable to a dark green piece of glass. The blue picture here shows it well (I used a bit of waste cloth/aida to get a pattern for demonstration, placed below the chips. Just know that the green at full-color is more transparent than this picture lets out).

I mixed these colors with Fuse Master's recommended "Water based medium" for painting, because I wanted to eliminate as many variables as possible. Oddly the ingredients list alcohol, and when I used the "few drops" suggested, it had almost no grip whatsoever. In the future I may try this with gum arabic, and I have an unfired test chip of the colors on opaque glass.

I started with the green half, for no particular reason, and applied the paint and blended with my badger blender. Then I began scratching out the clear and blue areas. I fired two layers of green, trying to build up to the emerald tone I was looking for. I switched to blue at one point, and simultaneously realized I could likely get sharper lines by using a mask to block out the design. So I did... mid piece.

Two layers of green enamel, just before I laid out the blue.

Lifting the mask from under the blue enamel

Unfortunately I realized one problem too late: the lines on the green portion are less clean, and the rays of the mullet (star) are shorter on that end. I scratched them out by slowly easing out to the edges of the shape and looking for the tracing template beneath the glass. It caused some inexact shapes. The rays created with the mask (which was copied directly off the template) were sharper and longer (more exact to the pattern) but thus different. The differences are a bit more apparent in some pictures. This is the piece going in for a firing:

You can see that the blue-side rays are stronger than the green side's. Here is another shot, while I was cleaning up the blue enamel before firing:

I worked on the laurel wreath at this point. I took the original image Estelle liked and tweaked it so that the cut lines would be evenly on the 45 degree marks. The original had an irregular spacing I don't care for. Here are the leaves painted, before firing:

The one on the right hasn't been cleaned up yet.

I'm still working on good brush technique, but after awhile I got a groove while painting these leaves. I was pretty pleased with how the lines were taking the exact form I wanted, the paint was mixed right where I wanted it. And once I had applied mat paint and begun shading:

The central roundel had three coats of green, and two coats of blue. I don't know if the blue is stronger naturally, or if I had just applied it heavier, but I didn't feel the need to try for more layers of it.

I noticed that the template gave me some grief while blending. The paint could pool a little more right alongside the template, and various variations on blending didn't alleviate that. In a high quality picture or in person you can see a slightly darker outline right along the edge of the mullet/star's rays on the blue side. I came to two realizations; I need larger palettes to get my paint mixed appropriately, and I should try and use a stencil (a suggestion from Molly)

The 3-green and 2-blue piece. I noticed that the enamels appear significantly darker against the opaque stone than when back-lit, prompting me to prepare test chips on opaque glass. I suspect that will give a richer color with fewer layers/firings. Update to follow.


I used my typical silver stain, fired to 1000 as usual. I had washed my other silver stain-only badger blender to improve its performance. I blended the stain but I thought at the time it wasn't as even as I liked. I wasn't sure if I used too little oil (my preferred stain medium) or my blending was poor. Either way, the results were shocking on two fronts:

Firing the piece to 1000 yielded a green that was blotchier than before (the green looked fairly regular), olive, and almost opaque. I was very unpleasantly surprised. I was also unhappy with the uneven stain. I decided to add more stain to try and balance it out, but was unsure about the green enamel. The blue didn't react poorly. I suspected that the green did not like the lower firing, but I didn't expect it to change. Firing it back up to 1250 (This brand of enamels indicate they can be used anywhere above a given range, and may be used while slumping etc, so I used my normal vitreous paint program) would overfire the silver stain, but might fix the green. I decided I would rather have overfired silver stain than keep the green, which I considered a totally unrecoverable mistake.

I was right on both accounts. I couldn't fix the uneven staining with more stain, and over firing it did exactly what was expected and created a darker stain and the characteristic mother-of -pearl scum. It's only visible in reflected light, so once the panel is in her window hopefully it's not as noticeable. Someone has suggested they will hold the scroll up in Midrealm court during Pennsic--the thought is mildly horrifying :)

I had a good talk with my Laurel about how to install the glass into the frame, as I didn't have the framing buttons that came with the oak frame. I settled on caulk (which was handy as I later needed to repair a trailer mirror for a friend and used it again).

After I handed it to Estelle, she pointed out I had caulked it into the frame backwards. *SIGH*. Fortunately an easy fix.

The completed scroll. Click for super-big picture.

Lessons Learned

The haze. It's not purple.

• A mask creates beautiful results, but needs to be used from the beginning for consistency.
• Molly suggested that I try and use a stencil instead of a mask (covering the opposite portion). That hadn't occurred to me, but is worth a try! That would enable me to blend evenly and avoid the "dark halo" the mask caused.
• Don't skimp on paint or stain and blend gently trying to conserve it.  Slather it on and blend it like a daiquiri that owes you money.
• Center painted borders a bit better (that is, double-check the design you are copying :) )
• Multiple firings might be changing the shape of the glass. Discuss with others...
• Watch carefully when you are clearing away matted paint/enamel. I've never noticed this problem before, so I wonder if it might be tied to enamels/this brand of enamels/this brand of enamels' weird alcohol-containing "water-based medium" but after clearing it away there was a haze of it left behind. I caught it via reflected light at one point, and had to get Q-tips and start really cleaning the glass for fear it would fire in and be visible. If you look closely you can see it in this picture, near the top

• A thought I had after is that, since the enamels say they mature somewhere around "1075-1150+" (I find it odd to give a range, and then 'or higher but...') with more time I could have tested firing the stain and enamel to a lower temperature that might not have treated the stain so badly, but which would have still given translucent enamel.
• As if I needed another reminder, you can't use a poor cut-line think "I can just make it work" because then you recut the project :)

Book Hoard: Stained Glass Primer Volumes 1 and 2

While teaching "Glass Cutting - All Levels" with Molly at Pennsic, she mentioned two books she recommends for new glass artists, different from the one I usually recommend. I grabbed them this week to look over.

Stained Glass Primer (Vol 1): The Basic Skills
Peter Mollica
4/5
All around an excellent book, in my opinion. As Molly had told our students, it IS dated. He described, at depth, the creation of leaded panels, and gives an overview of copper foil technique. His glossary is worth a read in it's own right. The dated portions are the tools and chemistry (well, and the typewritten text); he uses tools that are very traditional, and I think most people learning today use newer versions (lead cutting pliers instead of a lead knife, for example). He also references oleic acid as a flux, which works fine but is greasy and hard to clean up. More modern chemistry provides fluxes that are much easier to clean. The technique was all good, however! I appreciate the fact that he prefaces the book with "There are many alternatives, but this is what works for me" in essence. A skinny but packed book, I read it in under an hour.


Stained Glass Primer (Vol. 2): Advanced Skills and Annotated Bibliography
Peter Mollica
4/5
Also an excellent book. This one covers painting and staining heavily (Me being me, I noticed his date for the discovery of silver stain was 100+ years late. Research is a LOT easier for me today than it was for him in the 70s though!). He covers actually installing your window, which I've never seen before and, frankly, has always been a mystery for me. I've never tried to fit an existing embrasure because I had no idea how to do it and no one seems to cover it. He also discusses reinforcing, saddlebars, etc that is of definite interest to a SCAdian glassworker. He gives a recipe for easel wax but I'm not going anywhere near it...

He has some interesting books in his bibliography. I look forward to ordering some of them, too! Have to make Amazon Prime worth it.

Making a hogs-bristle brush

I had some trouble when I tried making my first minever paint brush.

I researched it a bit more and discovered two things: The first set of quills I had purchased were mutants and had been cut short by the vendor and second, people working with quills usually soak them to make them softer.

Now, to be clear, in the directions on p. 40 of my copy of Cennini he doesn't say to soak the quills. His thread may have been stronger, his quills thinner-walled, or many other things. However it looks like fly-fishers and others using these quills today frequently soak them, so I gave that a try. That made the quills softer and suddenly able to take a bit of a "squeeze" that broke my thread with the first try. Not wanting to waste my precious supplies of stoat tails, I decided to try again using hogs-bristle (the other type of brush described by Cennini).

A feather from the first set (top) next to one from the second set. I hadn't realized the feather should have this chiseled tip the top one has. Comparatively the second set also have much more usable quill.

The process is pretty much exactly as described in the previous post. I have a pack of hog-bristle brushes that I bought for scrubs in my glass painting. I took an exceptionally large one for which I had a duplicate and took it apart to claim the bristles.

An interesting observation, the bristles have a "root" end. I'm not sure it's biolgically/cosmetically a "root" but one end will be thicker and stronger on a good bristle (I also don't know why these are bristles and not hairs, but I'm a glazier-turned-brushmaker not a biologist... yet). I found it important to try and line up the bristles so I knew which end was the thicker/stronger end.

I took my soaked quill and trimmed the very end off. I used a tapered stick "of other good wood" as Cennini calls for, and shoved the quill on as far as possible. I then grabbed a clump of bristles and shoved them in the other end. Cennini described sticking bristles/hairs in individually until you can't get any more of them. This is where it became a LOT easier to know which was the strong end, as that end wiggles in more easily.

This also makes some sense for retention purposes, I think. The portion of the bristles that is at the opening of the quill is somewhat thinner. You can sneak more bristles in. If you were to try and pull the bristles collectively, however, I think the thicker ends would jam and not come out in a clump.

I tied a knot with my waxed silk thread and could see the quill took the pressure a little better. My thread snapped, after I had gotten the knot tied. On a lark, taking a note from an old martial arts movie that "wet silk never breaks" (not true!) I soaked the thread. I continued tying another knot and doing a little wrapping (that was probably too loose). Its difficult to do all this with only two hands! Same thread, knot, wrapping on the other end to secure it to the stick.

The brush was a little wild, and as Cennini told me to, I trimmed it down a bit:

As a final step I dunked it back into water and made some practice strokes. I gently tried pulling the bristles and none came out. I wouldn't give them a serious tug, but I think this is a practical brush made exactly to the primary source's standards. We will see if it holds up to vitreous paint and silver stain, however!

When I teach my silver stain glass this Pennsic, I hope to give out small vials of stain. I'd love to make a dozen of these to give out too. It didn't take too long in the scheme of things and would be a nice touch!

Lessons Learned:

Hog bristles are much more clingy than stoat fur. When I dunked my bunches of bristles in water they immediately made a tight cluster. I had to work the fur with my fingers for a while to try and make a cohesive bundle. I think in general bristle brushes are going to be easier to make than stoat.

I'm not sure why soaking a hard protein-based quill makes it softer, but don't our fingernails do the same after a hot soak in the tub? Might be something to investigate when bored later.

I have typed and said Cennini's name so much lately I'm starting to feel bad that I have no idea how to pronounce it. Keh-nee-nee? Cheh-nee-nee? I highly doubt it's Sen-nee-nee. I'll need to figure that out before I teach and have to say it several times.

Pennsic Lanterns [was: Placeholder til After Pennsic!]

[Edit 8/5/13]:

 I was making two lamps for Pennsic:

 Painting the bills and the coronets. This was commissioned for someone who has a rubber duck motif. The coronet is directly traced from a picture of her actual coronet. It didn't dawn on me at this time that I was leaving off the eyes.

The panels in a window, after being silver stained. The eyes are a tad spooky.

A quick-and-dirty glued-paneled lantern for Rudolph Tomasson for Pennsic.

[Original Post, 7/1/13:]
This is a placeholder for a post I can publish after Pennsic! Until then...

Pennsic Lantern

I want a nice-looking light source for Pennsic, although I'm going to keep it modern and electric. I have a thing for lanterns, but the two hanging for decoration around the house (with LED candles) aren't suitable for.... <evil Russian accent> Enhancement....</accent>. This made for a nice, and quick project.

I was passing through Menards and found these decorative lamps on sale, with a hinged door, for $10. I opened it up and immediately saw the four glass panes are held in by bendable metal tabs.

 

I took it home and bent out the tabs to discover that the pieces are also held in place by a strip of foam adhesive, kind of like what you'd mount a poster with (if you had no regard for the quality of the posters). My plan was to replace the two side panes with Midrealm Pales and the door (back) with mirror, to channel the light out the front. So, with that in mind, I took my glass cutter, scored horizontal lines across them, and smashed out the glass.

I used pliers to remove the shards and the foam adhesive strips. Then I cut strips of glue chip glass. I don't want lead lines impeding the light coming out of the lanterns, so I laid them on my lightbox and used a clear silicon adhesive/sealant to glue them together.

I cut a piece of mirror for the door and glued it into place, along with squares for the inside ceiling and floor, again to channel the light.

Once the silicone sealant was solid enough, I popped the panes into the sides and closed up all the tabs. Lantern done! I intend to take a bright flashlight and put it in the lantern, possibly rigging a switch near the handle on top.