Stress Testing - How?

 This is a presentation I gave a while ago on why and how to test for stress without risking the piece, that is, non-destructive testing.

How can I Release Glass Trapped in Casting Moulds?

How to get stuck glass out of a reusable mould?

The material is important to the method of removing stuck glass.

• Metal expands and contracts more than glass.

• Ceramic expands and contracts less than glass.

Mechanical methods

• Metal moulds can be hit relatively hard to break the contact between the mould and glass.

• Ceramic moulds should have only gentle taps, as they are more fragile than metal.

• If the glass is stuck, but moveable within the mould. It may be possible to wiggle the glass and mould against each other, which after a time may wear away the contact points and release the glass.

• Do not try to pry the glass from the mould. It is likely one or the other will break.

• Destructive method is to break the mould or the glass, which ever is the least important.

Contrasting temperature methods

Drape over metal –

• The metal contracts more than the glass, so placing the two in the freezer is one possible approach.

• Alternatively, heat the glass with hot water

• A third method is to place the drape upside down in the kiln and take it up to slumping temperature. Peek to determine when the glass has relaxed enough to be free from the mould. If the release temperature is above the annealing point, anneal again as before.

Drape over ceramic -

• The glass contracts more than the ceramic, so heating the glass with hot water may provide enough expansion to release from the mould.

• Or place the drape upside down in the kiln and take it up toward the slumping temperature. Peek to determine when the glass is released and skip to the anneal and cool process.

Slump into metal -

• The metal contracts more than the metal, so heat treatments will work best.

• Apply hot water to the metal until the glass is freed.

• Place the mould upside down on short posts and fire until the glass drops out. If the annealing temperature is exceeded, anneal again.

• Bang the metal mould with a rubber mallet. This risks breaking the glass, of course.

• Freezing only tightens the hold of the metal to the glass.

Slump into ceramic -

• The glass contracts more than the ceramic, so cold can work.

• Usually, glass sticking to a ceramic mould is a result of insufficient coverage of the mould with the separator.

• Placing the mould and glass in the freezer for a few hours may allow the glass to contract enough to be freed when taken out.

• Place the mould upside down supported on short posts. Set the firing to go to fusing temperature. Monitor with quick peeks from the slump temperature at regular intervals. When it drops, skip to the anneal process.

• Firing to a high temperature does not always release all of the glass.

Using adequate and appropriate separators to avoid trapping the mould or the glass need to be used to prevent the need to employ these release methods.

How can I Insulate Reactive Colours?

Sometimes the ideal colours for your project are reactive with each other, but a reaction line, or area, is undesirable.

Bob Leatherbarrow has demonstrated the possibility of avoiding the reaction. This works most clearly when using frit to blend one colour into another. Lay down the first reactive colour, then add clear frit or powder to cover the overlap area before adding the second reactive colour. The clear separates the two, but does not interfere with the transition or blending because the two colours cannot interact.

It is less easy with sheets of glass where you want to avoid a reaction line. In these cases you want to have a small but consistent gap between the reactive pieces. Place the glass with the gap and fill it with clear powder or fine frit to inhibit the reaction. You will need some experimentation to determine the necessary space between the glasses to avoid the reaction line without allowing a lot of light through, or the base glass showing as a line instead of the reaction line. After this you may decide that the reaction line is not so bad anyway!

How to make plinths for Fairs?

 Artist-led exhibitions make me realise why we pay commissions to galleries.

I spent a whole of a day making table-like plinths for the exhibition.

These are simple objects that require stability, must be plain to avoid competing with the object(s) on it, and - in our case - must be flexible and easy to store.

Based on two different design suggestions, I have constructed a table supported -but not attached - on a pair of right angle support legs. These legs are hinged so the whole can be closed and stored flat. As the legs are hinged, each pair can be combined to form a square plinth with the addition of a top.

The process of construction is simple too - although it does take time. The four I made took most of the day with the usual interruptions.

First you use a butt hinge to make the right angle supports. This is arranged so the support cannot open beyond a right angle:

When this pair of supports is screwed together, you place them on the up-turned top and place battens round the supports for security:

Finally, turn upright and paint.

Nuclear Waste Vitrification

 

vitrification process

Image credit: radopactovotu/eu.com

Expanding Nuclear Waste Vitrification Strategies with Customizable Glass

by Rebecca Straw.

Nuclear power plays a key role in sustainable energy generation, offering a long-term solution with its extended operating life and low greenhouse gas emissions. As of 2025, nuclear energy supplies approximately 10% of the world’s electricity, with 440 power reactors operating across 31 countries.¹

Beyond power generation, nuclear technology is also starting to play a vital role in medical diagnostics, industrial processes, and space exploration. With growing demand for reliable, clean energy, the sector continues to expand, with new reactors under construction worldwide.² However, nuclear waste disposal remains a critical challenge, requiring innovative solutions to ensure long-term safety.

Vitrification and the Growing Importance of Nuclear Waste Management

High-level nuclear waste (HLW) is the most hazardous by-product of nuclear energy production, consisting primarily of spent nuclear fuel and its reprocessed liquids. Its long-lived isotopes and high radiation levels pose significant environmental and health risks, requiring robust containment strategies.^3,4

As unstable isotopes decay, HLW continuously emits heat and radiation, making secure storage essential to prevent environmental contamination.⁴ Certain radionuclides, such as the actinides plutonium and curium, have extremely long half-lives, necessitating immobilization techniques that ensure stability for thousands of years.³ Others, like Technetium-99 and Iodine-129, are highly soluble in water, increasing the risk of groundwater infiltration if not properly contained. These challenges demand a waste form that offers long-term durability, leach resistance, and mechanical stability under repository conditions.

Vitrification—the process of turning waste into glass—has emerged as one of the most effective containment methods for HLW.⁴ Unlike dilution or surface storage, vitrification permanently traps hazardous materials within a stable glass matrix, preventing their release into the environment. Additionally, vitrified waste is compact, insoluble, and well-suited for secure long-term storage and disposal.

Glass Selection in Nuclear Waste Immobilization

Selecting the right glass composition is critical for the success of vitrification. Borosilicate and phosphate-based glasses are the two primary materials used for HLW immobilization.

Borosilicate glass is favored for its high chemical durability, low thermal expansion, and capacity to incorporate a wide range of radionuclides.³ It has been the standard choice in countries like France, the UK, and the US, where large-scale vitrification facilities are in operation. Its success is largely due to its compatibility with various waste cations, well-characterized structure, and well-established processing technology.³

However, optimizing the waste loading—the percentage of waste incorporated per unit volume of glass—while ensuring the final product remains stable and processable remains a persistent challenge in vitrification processes. While increasing waste loading reduces overall storage costs and processing time, it requires precise control over the glass formulation to prevent crystallization or phase separation.

Optimized borosilicate glass is generally well suited for this purpose, but certain waste components present in HLW, such as molybdenum and noble metals, have low solubility in the borosilicate matrices, limiting how much can be incorporated, and its utility as a universal HLW matrix.

Expanding Vitrification Strategies Through Customizable and Alternative Glass Solutions

While borosilicate glass has long been the standard for HLW vitrification, its limitations in incorporating certain waste components have driven the exploration of alternative glass formulations. Phosphate-based glasses (e.g., iron phosphate, alumino phosphate) present a promising alternative to traditional borosilicate glass for the immobilization of HLW, particularly in the management of actinides, lanthanides, and other elements that are poorly soluble in borosilicate.

These phosphate glasses offer enhanced degradation resistance and superior tolerance to radiation, making them ideal for managing complex waste streams.³ In particular, phosphate-based formulations are highly relevant for next-generation reactor technologies, such as molten salt reactors. These reactors, which utilize liquid fuel salts, produce waste compositions that are rich in fluorine and differ significantly from those of conventional reactors, thus limiting the types of glasses that can effectively immobilize this type of waste.⁵

 Phosphate glasses also stand out for their ability to better accommodate halide-rich waste streams. These glasses can be processed at lower temperatures, reducing volatility, and can accommodate higher salt loading, making them an attractive solution for waste from advanced reactor designs. ⁵ For example, fast breeder reactors, which generate waste with high concentrations of plutonium and actinides, require non-silicate glass forms capable of accommodating these elements without compromising long-term integrity. 

Leading Innovation in Nuclear Waste Vitrification

MO SCI is pioneering the development of advanced glass formulations that improve waste loading and long-term performance while addressing the limitations of traditional glass forms. By focusing on customizing glass compositions to suit specific waste characteristics, MO SCI is helping to ensure that vitrification remains a scalable and effective solution for HLW disposal, supporting the transition to next-generation reactor technologies.

For further information on nuclear waste management solutions, please contact us today. 

Rebecca Straw

References and Further Reading

1. World Nuclear Association. Nuclear Power in the World Today [Updated 6 Jan 2025]. Available from: https://world-nuclear.org/information-library/current-and-future-generation/nuclear-power-in-the-world-today#:~:text=Nuclear%20energy%20now%20provides%20about,in%20about%20220%20research%20reactors.; (Accessed on 3 Mar).

2. Hyatt NC, Ojovan MI. (2019) Special Issue: Materials for Nuclear Waste Immobilization. Materials (Basel);12(21).

3. Bohre A, Avasthi K, Pet’kov VI. (2017) Vitreous and crystalline phosphate high level waste matrices: Present status and future challenges. Journal of Industrial and Engineering Chemistry;50:1-14.

4. Sanito RC, Bernuy-Zumaeta M, You SJ, Wang YF. (2022) A review on vitrification technologies of hazardous waste. J Environ Manage;316:115243.

5. Riley BJ, McFarlane J, DelCul GD, Vienna JD, Contescu CI, Forsberg CW. (2019) Molten salt reactor waste and effluent management strategies: A review. Nuclear Engineering and Design;345:94-109.

The Effect of Glass Temperature on Cutting

There are many opinions on how glass cuts when cold.  Some report cutting outdoors in sub-freezing temperatures, others that only warm glass cuts well.  I decided to see what scientific information there may be on this idea.

The Science

The scientific literature mostly concentrates on the effects at higher temperatures than we are concerned with.  However, there are some things that are applicable, and some of these effects of temperature are outlined below.

·         High humidity results in loss of strength. 

·         The strength of glass is reduced by 25% at 100°C compared to 0°C.

·         Glass needs several days to be at an even temperature throughout.

·         Variance in temperature across the glass causes unwanted breakages.

·         Colder glass becomes more brittle due to loss of elasticity.

·         Hardness of glass increases with decreasing temperature.

The terms of strength, hardness and brittleness have scientific definitions that are hard to apply to the everyday glass cutting that we do.  Strength may or may not have applicability to glass cutting.  Elasticity may or may not be an important factor in cutting.  Surface hardness may play a part in cutting while cold.

Applicability of the Science

However some things seem to apply. 

High humidity results in loss of strength.  This may be a factor in low temperature cutting.  The humidity in a relatively closed environment increases with the reduction in temperature.  Breaking glass is about the creation of a weakness in the glass along the score line.  In so far as strength is a factor in the break running along the score line, this may be an element in cold glass cutting.  If the whole glass is weaker, the difference in strength at the score line is less and so promotes unwanted breaks.

Variance of the temperature of the glass throughout the substance of the glass promotes unwanted breakages.  Perhaps the cold glass that is difficult to cut is not equally cold throughout.  Certainly a number of people report that they store their large glass outdoors and can still score and break the glass during the winter perfectly well before bringing it into the studio. 

Glass becomes more brittle with decreasing temperature, and it also becomes harder.  Perhaps these two elements are a factor in controlling breakages.  If the glass is both harder and more brittle, a different scoring method is required. 

The way in which glass at any temperature breaks is related to the force of the score, the speed of the score and the angle of the cutting wheel.  If the glass is both harder (at the surface) and more brittle it requires less scoring force or a blunter wheel angle.  The more blunt the wheel on a thicker (i.e. stronger) glass, the more vertical the stress lines are created in the glass.  So in a cold and harder glass, a blunter wheel angle seems appropriate, even though the glass is not thicker.

It is not usual for people to have cutting wheels of different angles, so an easier, although more skilled, approach is to reduce the scoring force in cold conditions.  Reducing the force in scoring a hard and brittle glass causes the stress lines to be more vertical than increased forces do.  Increased forces cause lateral lines of stress to be created, leading to unwanted breakages.

Secondly, the glass being more brittle, less force in breaking stress is required.  As the glass becomes colder, the less elastic it is.  This elasticity is an important element in breaking the glass at room temperatures. The score needs to be run gently to counteract the loss of elasticity and the consequent increase in the brittle strength of the glass.

Conclusions

My conclusion, after the reading I’ve done, is that cold glass becomes slightly stronger and more brittle than room temperature glass, and so requires a slightly different method of cutting. This difference is to reduce the pressure of scoring and the force of breaking (applying stress to the glass).  

An alternative conclusion by Dennis Brady is that his tests showed that the difference between cold glass and warming for 5 minutes in an electric blanket produced the following effects:

"Float glass no difference.

Transparent art glass no difference.

Opal or streaked glass definite difference.

Machine rolled less difference than hand rolled."

His conclusion was that the "lower viscosity of opalescent glass made it less likely to follow a score when cold."

Of course you can warm the glass up before scoring it, but the research seems to indicate that only opalescent glass will benefit from heating.

Revised 25.12.25

Glass Coatings for Batteries

 

Using Glass to Optomize Composite Materials for Battery Applications

by Rebecca Straw

Polymer-based resins, such as epoxy, polyurethane, and silicone, are commonly used for sealing and potting applications in batteries. By filling voids within a battery enclosure, these materials help to promote heat dissipation and electrical insulation while offering protection against mechanical stress, chemical exposure, and moisture.¹

Although resins are valued for these properties, they can exhibit inherent limitations when used alone.² For this reason, achieving optimal performance in potting adhesives has been a significant challenge over the past decade. This includes meeting requirements like low dielectric loss, enhanced shock resistance, high thermal conductivity, and stable weight.³

Enter composite materials: By integrating glass components—such as glass fibers, and hollow or solid glass microspheres, —it is possible to create a composite material with superior thermomechanical, structural, and electrical performance.⁴

Glass Fibers: Reinforcing Strength and Sustainability

Glass fibers are made from extremely fine strands of non-crystalline glass. They are highly valued for their excellent surface-area-to-weight ratio, and the amorphous nature of glass ensures that its properties remain consistent throughout the fiber.^4,5 When mixed with epoxy, these composites are widely utilized in structural applications and valued for their outstanding mechanical properties –⁶

In battery applications, these attributes bolster the composite’s capacity to endure mechanical shocks and vibrations, thereby improving overall durability and reliability. Additionally, the option to use recycled glass fibers contributes to sustainability by reducing waste, aligning with the industry’s push toward circular economy practices.⁴

Hollow and Solid Glass Microspheres: Lightweight Innovation with Multifunctional Benefits

Hollow glass microspheres, also known as microballoons, are thin-walled glass bubbles containing a void in the center. The balloon sizes generally range from 10 to 90 microns, and they have low density, high crush strength, and chemical durability.  Their shape and smooth surface minimize stress concentrations at the interface between the fillers and the matrix, enhancing structural integrity. When used in resins, they create polymer composites with augmented thermal and sound insulation, reduced weight, and improved fracture toughness, making them ideal for advanced applications.^7,8

Solid glass microspheres are spherical particles made from glass, These particulates are valued as fillers in polymer composites due to their unique properties, including customized thermal conductivity, isotropy, smooth spherical surfaces, and minimal stress concentration at the filler-matrix interface. Their uniform shape guarantees consistent shrinkage and enhances the processability of filled materials, while also minimizing orientation effects during molding.^11,12

In battery potting applications, engineered solid glass microspheres can boost insulation performance, increase thermal conductivity, and ensure dependable material properties, making them particularly suitable for protecting sensitive components.

Silane Coatings: Seamlessly Bonding Glass and Polymer for Superior Composites

Silanization is a surface modification technique used to increase the interfacial adhesion between glass particulates, such as microspheres and fibers, and polymer resins in composite materials. By applying silane coupling agents, a strong chemical bond is formed between the glass and the polymer, significantly improving the mechanical properties, loading capabilities, and surface adhesion of the composite.¹³

Silanization has also been shown to protect glass fibers from mechanical damage during processing and environmental degradation, making it particularly beneficial for battery potting applications.⁴

Tailored Glass Solutions from MO SCI

By integrating glass materials into polymer resins, researchers can create composites that meet the stringent demands of modern battery technology and contribute to greater sustainability and safety.

MO SCI’s expertise in producing high-performance glass fibers and microspheres, coupled with advanced silane coating technologies, ensures that customers have access to tailored solutions for optimizing battery potting and sealing materials.^14,15

Contact us today to discuss your material performance requirements.

References and Further Reading

1. Epec. [Online] Battery Potting & Encapsulation. Available at: https://www.epectec.com/batteries/potting-and-encapsulation.html (Accessed on 21 November 2024).

2. Yang, L., et al. (2024). Characterization of Potting Epoxy Resins Performance Parameters Based on a Viscoelastic Constitutive Model. doi.org/10.3390/polym16070930

3. Hu, J.B. (2020). High-performance ceramic/epoxy composite adhesives enabled by rational ceramic bandgaps. Scientific Reports. doi.org/10.1038/s41598-019-57074-7

4. Săftoiu, G-V., et al. (2024). Glass Fibre-Reinforced Composite Materials Used in the Aeronautical Transport Sector: A Critical Circular Economy Point of View. Sustainability. doi.org/10.3390/su16114632

5. Park, S-J., et al. (2011). Chapter 6 – Element and Processing. Interface Science and Technology. doi.org/10.1016/B978-0-12-375049-5.00006-2

6. Safi, S., et al. (2016). Evaluation of interfacial properties of the silane blend sized glass fiber–epoxy composite by the microdroplet test. Journal of Composite Materials. doi.org/10.1177/0021998316661620

7. Liang, J-Z., et al. (2014). Estimation of thermal conductivity for polypropylene/hollow glass bead composites. Composites Part B: Engineering. doi.org/10.1016/j.compositesb.2013.08.072

8. Wouterson, E.M., et al. (2004). Fracture and Impact Toughness of Syntactic Foam*. Journal of Cellular Plastics. doi.org10.1177/0021955×04041960

9. Mo Sci. [Online] Porous Silica. Available at: https://mo-sci.com/products/porous-silica/ (Accessed on 21 November 2024). 

10. Li, M., et al. (2024). Preparation of DOPO-KH550 modified hollow glass microspheres/PVA composite aerogel for thermal insulation and flame retardancy. Journal of Colloid and Interface Science. doi.org/10.1016/j.jcis.2023.10.073

11. Mallick, P.K. (2000). 2.09 – Particulate and Short Fiber Reinforced Polymer Composites. Comprehensive Composite Materials. doi.org/10.1016/B0-08-042993-9/00085-1

12. Mishra, D., et al. (2016). An experimental investigation on the effect of particle size on the thermal properties and void content of Solid Glass Microsphere filled epoxy Composites. IOP Conf. Series: Materials Science and Engineering. doi.org/10.1088/1757-899X/115/1/012011

13. Perdum, A-I., et al. (2022). HOLLOW GLASS MICROSPHERES TREATED WITH SILANE COUPLING AGENT. University Politehnica of Bucharest Scientific Bulletin, Series B. ISSN 1454-2331.

14. Mo Sci. [Online] Glass Microspheres. Available at: https://mo-sci.com/products/glass-microspheres/ (Accessed on 21 November 2024).

15. Mo Sci. [Online] Custom Development Services. Available at: https://mo-sci.com/services/custom-development-services/ (Accessed on 21 November 2024).

Why do Bubbles Appear in a Circle?

Example used with the maker’s permission

Piece in kiln ready to fire

Description of the piece.

A commissioned piece made up of Bullseye glass, 38cm/15” diameter, 3mm base with 2 and 3mm strips laid on top to a 6mm maximum depth, fired on a “standard” full fuse at 795°C/1463°F, annealed for 3.5 hours. The piece took up the whole of a newly primed shelf.

The fired piece 

The fired piece developed an off centre bubble, and when the piece was cooled it rocked. The shelf was checked and it was level.  

Previous firings of similar projects were mostly successful, but one was not, although felt to be interesting:

The piece bubbled and various sized holes were randomly drilled to determine the effect.

Other successful pieces were only slightly smaller:

The question was what to do to recover the piece, and why did it happen. Previous bowl blanks on the same program were ok, although this one was larger.

My Response:

The layup is the problem. A thinner (single?) layer in centre surrounded by radiating strips will trap air in the interior and so create bubbles.  This kind of layup needs to have 1 - 3 mm fibre paper topped with shelf paper, under this kind of piece to allow air out.

This is a commission, so a repair is not acceptable. A new one needs to be created, because there would be reputational damage by passing off a repair that will inevitably show evidence of the fault. In general, repairs are unsuccessful.  Repurposing the glass is a better solution.

Other possible causes in addition to the lay up are:

When a piece rocks on a flat surface it has become bowed, and it is evidence of stress developing during the annealing cool.

The annealing and cooling were likely to be inadequate – too short a soak, too fast a cool, or both.

In this case, the anneal soak was certainly long enough, so too fast a cool is the likely cause of the bowing.

The nearness of the glass to the kiln walls is often a cause of uneven heating, although in this case it did not become a problem.

It is also possible that the additional diameter was enough to push a barely adequate bubble squeeze beyond the possibility of full elimination of air from under the glass.

As a result of the experience of the “moonscape”, variously sized holes were randomly randomly around the centre of the bubbled piece to determine if that would have been an acceptable fix. The thicker ring around the burst large bubble remained in the attempt at a fix.

Holes drilled randomly and extra clear dots were added.

The client was contacted to explain the accident and to confirm the making of another.

Why do Ground Edges Appear on the Surface of the Glass?

"Why do the ground edges of my glass appear on top of the glass?"

The scum from grinding edges, which promotes devitrification, often appears in in fusing. But why does it appear on the surface? 

There is a lot of movement of glass edges during a firing. On the way up in temperature, the glass is relatively stiff and expands with a vertical edge during most of this phase.  At the top temperature the surface is expanding and pushes the edge flat to the separator.  Then, as the temperature falls the cooling glass surface contracts, pulling the edge to the surface together with anything it has collected from the separator.  Sometimes, cleaning the ground surface is not enough to prevent the rough surface from picking up some of the separator, and this is what is seen in the final product.

If you are going to grind to fit the glass pieces, you need to finish with a fine grinder bit. These are usually around 220 grit which might be fine enough if cleaned well, but run some tests to be sure. The safer grit to prevent the scum is 400, but the ground glass surface still needs to be scrubbed clean.

There are good reasons to avoid grinding, or when not avoidable, to fill gaps with powder or frit of the same colour.