Hot-Melt Adhesive

Some people have begun using glue guns to stabilise their glass before transporting to the kiln.  These use glue sticks which are a hot melt adhesive.

Hot melt adhesive, or hot glue, is a form of thermoplastic.  It is commonly sold in solid cylindrical sticks of various diameters designed to be applied using a hot glue gun. The gun uses a heating element to melt the plastic glue. The glue is tacky when hot, and solidifies in a few seconds to a minute. The glue squeezed out of the heated nozzle is initially hot enough to burn and even blister skin.

The glue sticks are available in a variety of melt temperatures.  The standard and most commonly available glue sticks are white to cream in colour and the guns have an orange applicator.  The hot glue is delivered from non-adjustable guns at about 195°C.  This is hot enough to burn skin and the possibility of heat shocking the glass should be considered.

3M make a low temperature variety of hot melt adhesive which needs low temperature glue guns – the 3M version is blue, and the sticks contain LT as the suffix to the part number.  This is applied at 129°C.  This is still hot enough to burn skin, but possibly with less risk of thermal shock to the glass.

The risks of breaking the glass from the heat of the glue is one of the risks.   The greater risk is of the effects of the thermo plastic on the surface of the glass.  The glue is a plastic. All of us who have left a plastic item in the kiln can witness to the black smoke created.  So, it won’t do your kiln much good, and will require firing empty to burn out all of the plastic residue. 

It also will not do you glass much good.  The thermo plastic melts and will vaporise at some (unknown) temperature.  But it will leave a residue for the process of devitrification to develop.

My recommendation is to avoid the use of hot melt adhesives for anything going into the kiln.  It is most likely to cause difficulties with the kiln and the glass.

Controlled Pore Glass Manufacturing and Applications

 

Controlled Pore Glass Manufacturing and Applications

Posted Krista Grayson on Oct 29, 2020

Controlled pore glass (CPG) is a high-silica glass that contains pores with a specific size distribution. Porous glasses can be made into a wide range of geometric forms (such as frit, rods, plates, beads, and hollow spheres), and pore sizes can be precisely tuned from the range of angstroms to millimeters. Controlling pore size means that the physical and chemical reactivity of the glass with gases and liquids can be tailored to specific applications such as chromatography, sensing, and filtering.

In addition to this, porous glasses exhibit high mechanical strength, chemical durability, and thermal stability; which make them superior to other porous media (such as polymers and ceramics) for a variety of applications.1

This article covers how porous glass is made, how pore size can be controlled, and some of the varied applications of this unique material. 

Manufacturing Porous Glass

Porous glass can be manufactured via several different routes, each of which produces different characteristic pore structures. The most common methods involve phase separation or immiscibility of alkali borosilicate glass.

Producing controlled pore glass via the alkali borosilicate system

Alkali borosilicate glass systems consist of a silica glass-former with borate and alkali-oxide additives used to lower the melting temperature of the mixture and impart other properties. In other terms, alkali borosilicate systems are mixtures consisting of the chemical species SiO2, B2O3, and R2O; where R is sodium, potassium, or lithium.

Simplified ternary phase diagram for the Na2O–B2O3–SiO2 system. The “Vycor” region corresponds to the phase separable mixtures that can be used to manufacture porous glass. (Bartl et al., 2001)

Schematic showing the formation of porous glass from a phase separated alkali (sodium) borosilicate mixture. (Hasanuzzaman et al 2016)

When the constituents of this mixture are tuned to specific concentrations and heated, the entire mixture undergoes an amorphous phase separation: the mixture transforms into two distinct phases.

One of these phases is an alkali-rich borate phase and the other a silica-rich glassy phase. Crucially, the borate phase is soluble in acid, while the silica phase is not. This means that, following heat treatment, the borate phase can be leached out with a hot acid solution. What remains is a highly pure and porous silica glass skeleton with large surface area: in other words, porous glass.

Controlling pore size

Acid-leaching of a phase-separated mixture generally results in a very narrow pore size distribution, earning the name “controlled-pore glass” and lending the resulting glasses to applications such as adsorptive chromatography of biomolecules.2

The average pore diameter is a function of heat treatment temperature and time, as well as glass composition. Thus, controlling the heat treatment temperature or time (or both) can easily produce porous glasses with a range of pore sizes to suit different applications. Glasses formed via these methods generally have pore diameters in the region of 1 to 1000 nm.3,4

Formation of porous glass using alkali borate systems can also be achieved without inducing a high-temperature phase separation: directly etching the surface of the glass can result in the formation of small pores (1-2 nm) restricted to the surface of the glass.

Other manufacturing routes

Porous glass can also be manufactured by glass sintering or via sol-gel routes. Glass sintering is widely used to produce glass foams with pore diameters in the region of 400 m to 1 mm. In sol-gel processes, a solution of organic monomers (sol) is turned into a glass by removal of the liquid phase. Sol-gel processes have been used successfully to create a range of pore sizes for different applications5,6 and they are becoming more common methods.

Applications of Porous Glasses

Porous glass provides an alternative to fused quartz which is comparatively difficult to produce and form into different geometries. However, many emerging applications make use of the functionality offered by the pores themselves. The high surface area and tailorable pore size distribution of these glasses make porous silica a highly effective filtering material, capable of separating not only the basis of molecular size but also of molecule type.7 This, along with a wide range of possible geometries, has made them useful in biosciences and chemistry.1

For example:

• Enzyme immobilization and size exclusion chromatography techniques have been developed using porous glass; making use of its extreme chemical inertness, optical transparency, and small pore diameters.5,8,9
• Surface-functionalization of controlled-pore glass using polyaniline has been used to develop optical chemosensors.10
• Using additives to finely tune the size of pores can result in functional size-selective catalyst supports.11,12
• The role of porous glass in targeted drug delivery has been studied, using porous-wall hollow glass microspheres. The spheres provide a porous, inert shell for the introduction and release of drugs inside the body.13
• Porous glass is also being investigated as a bio-scaffold. These applications make use of the porosity, strength, corrosion-resistance, and biocompatibility of porous glass.14,15

All of these applications are made possible by the tunability of pore size, which enables specific physical properties to be imparted in the glass during the manufacturing process.

Mo-Sci produces high purity (> 98% SiO2 and < 2% B2O3) porous glass frit and spheres suitable for applications in industry and research. Contact us to speak with one of our experts about your project requirements.

References and Further Reading

1. Hasanuzzaman, M., Rafferty, A., Sajjia, M. & Olabi, A.-G. Production and Treatment of Porous Glass Materials for Advanced Usage. in Reference Module in Materials Science and Materials Engineering (Elsevier, 2016). doi:10.1016/b978-0-12-803581-8.03999-0
2. Elmer, T. H. Porous and Reconstructed Glasses. in Engineered Materials Handbook (1992).
3. Zhu, B. et al. Synthesis and Applications of Porous Glass. J. Shanghai Jiaotong Univ. 24, 681–698 (2019).
4. Enke, D., Janowski, F. & Schwieger, W. Porous glasses in the 21st century-a short review. Microporous Mesoporous Mater. 60, 19–30 (2003).
5. Lubda, D., Cabrera, K., Nakanishi, K. & Minakuchi, H. SOL-GEL PRODUCTS NEWS Monolithic HPLC Silica Columns. Journal of Sol-Gel Science and Technology 23, (2002).
6. Baino, F., Fiume, E., Miola, M. & Verné, E. Bioactive sol-gel glasses: Processing, properties, and applications. Int. J. Appl. Ceram. Technol. 15, 841–860 (2018).
7. Hammel, J. J. & Allersma, T. United States Patent | Thermally stable and crush resistant microporous glass catalyst supports and methods of making. 923, 341 (1975).
8. Du, W. F., Kuraoka, K., Akai, T. & Yazawa, T. Effect of additive ZrO2 on spinodal phase separation and pore distribution of borosilicate glasses. J. Phys. Chem. B 105, 11949–11954 (2001).
9. Jungbauer, A. Chromatographic media for bioseparation. Journal of Chromatography A 1065, 3–12 (2005).
10. Sotomayor, P. T. et al. Construction and evaluation of an optical pH sensor based on polyaniline-porous Vycor glass nanocomposite. in Sensors and Actuators, B: Chemical 74, 157–162 (2001).
11. Takahashi, T., Yanagimoto, Y., Matsuoka, T. & Kai, T. Hydrogenation activity of benzenes on nickel catalysts supported on porous glass prepared from borosilicate glass with small amounts of metal oxides. Microporous Mater. 6, 189–194 (1996).
12. Gronchi, P., Kaddouri, A., Centola, P. & Del Rosso, R. Synthesis of nickel supported catalysts for hydrogen production by sol-gel method. in Journal of Sol-Gel Science and Technology 26, 843–846 (Springer, 2003).
13. Using Porous Glass Microspheres for Targeted Drug Delivery Mo-Sci Corporation. Available at: https://mo-sci.com/porous-glass-microsphers-targeted-drug-delivery/. (Accessed: 2nd September 2020)
14. Rahaman, M. N. et al. Bioactive glass in tissue engineering. Acta Biomater. 7, 2355–2373 (2011).
15. Fu, Q., Saiz, E. & Tomsia, A. P. Bioinspired strong and highly porous glass scaffolds. Adv. Funct. Mater. 21, 1058–1063 (2011).

Writing About your Business

Staying in touch with potential and existing customers is important to getting more sales.  This is especially true for websites.  You need to build an online relationship which is similar, but has a different expression, to in-person relationships.  You need develop your online business profile.  Whether you concentrate on craft fairs or wholesale and online sales, you need to communicate about what you do.  Whether you have a website with a shop or just a Facebook page, you need to tell people what you do to build support.

It may seem difficult at first to know what to write about your business that will be interesting to your customers and support sales and be worth the effort.  There are a lot of things you can say about your business.  When you begin to think of the elements for communication with your potential customers there are lots of things you can say that will interest them and give your business a personality and an interesting profile.

But I don’t have a web site.  I sell at craft fairs and to galleries.

This still applies to you.  You need to tell all sorts of people and organisations about your business.  You need to have something for galleries to look at.  You need copy for newspapers and other media.  You need a  statement about you and your business at craft fairs.  You need to use social media to get people to the physical sales points.  You need to think about how these elements can help provide interesting posts.  Of course, not all that is given here is directly applicable to personal interactions, but it will give you the direction you need to present yourself and your business in the best light.

There are lots of ideas to get you to thinking about what you can do to communicate.  What follows are indicators of what you can do. You don’t need to use them all, but employing a range of these elements will give variety and interest to your communications.  It may also, along the line, provide you with a much higher profile and incidentally, sales.  You do need to communicate regularly and consistently with the audience.  An irregular post every month or so, is not enough.  You may have to set a schedule for publishing communications to your followers.

Write -

- About your business

·        What started you in business? what was the inspiration? Talk about any greater purpose than simply making your items. What are your motivations to continue working? What gives you joy?

·        How, and why did you choose the business name? Who did you involve? How does the name continue to be appropriate?

·        Tell people what it is about you and your work that is special or unique.  Indicate what your niche is, make it explicit for your potential customers.

·        How do you do business? Do you take commissions?

·        Share the stories and case studies of your experiences.  For example, take people through the stages of a commission.  Telling about the changes, developments, challenges shows how you work.  Show the results and tell what the client liked most about it. This provides the opportunity to include testimonials.  Include lots of sketches, photos. Importantly, get the commissioner’s permission to share details.  

An example of a site which provides a number of testimonials: http://www.gilroystainedglass.com/gilroy/testimonials/

Another example is this blog which does everything – the way she works, her stories, information, inspirations and there is no obvert selling at all. https://morganica.com/about-me/

- About your Location

·        Tell people where you are located. This helps to increase trust.  Talk about why you chose the area. How does the place affect your work? Provide pictures of your specific location, the area, and elements of landscape or cityscape that interest you.

The Northlands Creative site gives you a sense of place. 

·        Essentially, offer a behind the scenes view of how your location interacts with your creativity.  An inner-city industrial area can be as interesting as the countryside.

An insight to working practice is given in the Bob Letherbarrow website. 

- About your inspirations

·        Talk about people that have inspired you, role models, influencers. What have you learned from them?

·        What events – personal and world-wide – affect your work? Write and illustrate them.

An artist statement example from Bob Leatherbarrow 

·        Write about the kinds of environment that influence elements of your work.

- About things that interest you

·        Reviews of exhibitions, events, books.

·        Share your passions, reveal your personality, what excites intrigues you about your craft.  Why your glass expression than others? Does your work tell stories? Do you have a bigger purpose in making your craft?

·        Write about what is important to you.  This shares your values, and by writing from different angles will bring more visitors to the site.  Recommending other small businesses with similar values not only creates a business community, but a customer community too.

- About the process

·        Share the creative process involved in your body of work.  It can  be in words or images, short videos. 

·        Show the design process – inspiration, sketches, prototypes, final items and then the results at shows.  Use lots of pictures.

- About useful information

·        Share information and guidance about looking after your products.

·        Give information about related businesses.  These will be services or products that you do not supply but are relevant and are provided by other local businesses.

·        General tips related to your area of business shows you are knowledgeable, helpful and trustworthy.

·        General tips on how to display, use or wear your work grab attention.  Pictures are especially important here. 

·        Write useful communications.  Think about what your ideal clients would find useful to know.  Is there any maintenance needed for your glass? How to clean the glass. Give practical advice and suggestions. 

·        Promote other resources or books you like. Avoid a sales post, just include a link to the relevant page of your site as a sign off.

·        Think about having guest writers.  Getting others to write occasionally for you saves you work.  Interviews are another way to vary the voice of your communications.  It is essential to be clear about what these guests are to focus on, and give them the opportunity to promote their own site.

- About your customers

·        Ask your followers specific questions, get them involved in new developments at an early, planning stage, rather than at the end.  This gets people committed early to your work and without any explicit sales pitch. 

·        You can ask about the barriers people have to buying from you or others.  You can get information about what publications, sources they use, by asking.  This can be done on social media, or via direct emails.

·        Answer clients’ questions quoting their words.  This can increase the visibility of your site by using others’ searches, so leading them and others to your site. 

·        Helpful responses create a trusted business source.

- About developments and news

·        Write about the events you are planning to attend. There needs to be a group of communications leading up to the event.  Lots of advance notice is needed for people to plan a visit.  To give this notice, you can produce a number of  notices: Lead them through your preparations, the development of your collections, background to the work you will be taking, show the packed van and the final show setup.  These six notices will involve potential customers and build their interest in coming to the event.

·        Tell the stories of the event. What happened, your best sellers, star purchasers, meetings with fellow exhibitors all provide interest to your customers. You can include links to your price list or catalogue in these communications.  This is much better than sending a bare list or catalogue.

·        Talk about your product of the week or month - why the design, what inspired it, how did you name it, what’s special about it.   Start with a good photo of the work.  Possibly add something special – free p&p, special price in combination with another item, etc., to attract a purchase.

- About outlets

·        Blog about your retailers and wholesalers.  It cements your relationships with them, by showing your commitment to supporting their business too.   It  provides publicity for your work. Photos of your work in the locations is good customer-assuring publicity.

·        Let other businesses know that you have sent out information about them.  It may get you reciprocal mentions.

·        Working with wholesalers has better results when directed to individuals or single companies.  Preparing introductory material that is relevant to the client and adding the relevant images, lists, catalogue, gets better results than generic approaches.

An example of telling people where your work is available in Steve Immerman's website. 

Of course you do not need to write about all of these elements all the time. But they form the background to what you write about your business, craft, current work, and to some extent your life.

Writing specific, focused, timely communications

·        Timely communications are important.  When are customers likely to buy? – send out things prior to that time.  Think about the reasons they might buy and include them.  Gift giving times (such as back to school, springtime, valentines, awareness days) are times for focused communications indicating what you have that is relevant to the event or occasion.

·        Send out notices of an upcoming event through all your communications sources in a kind of countdown to the event giving your activities toward the opening of the event or show.

·        Be consistent in the style of the communications.  Short, direct, and focused posts with lots of pictures are most likely to be read.  Handmade Lives says immediately what it is about (unfortunately now ceased). 

News vs. Newsletters

These communications are not newsletters. Who reads newsletters anyway?

• Stay updated https://www.thecoolhunter.co.uk/
• Use lots of photos.  Make the communications visual. E.g. https://www.designspiration.com/
• This site has busy visuals, but leads by images rather than words https://www.craftscotland.org/

All your posts and communications should be simple and direct.  They should be fairly short (unlike this post!) to be sure they are read.

In Summary

How do you put all this together?  This is an example of a blog which does everything – the way she works, her stories, information, inspirations and there is no obvert selling at all. https://morganica.com/about-me/

Writing about your business is more than just the business.  You are the business.  So, it is writing about you and what you do, not just a dry business description.  You have an advantage over big business. You have a personal story to tell.

The Annealing Range Concept

There is a lot written about the annealing temperature of a glass being at a single exact temperature. This is another fundamental misunderstanding of the concept - much like CoE meaning compatibility.

The annealing point is mathematically defined as the temperature at which a glass reaches a particular viscosity. This is the temperature at which stress can most quickly be relieved. It is denoted as Tg. Each glass has its own Tg according to colour and composition. The manufacturer recommends a good average Tg for their glass. The first section of this blog post gives a description of the glass transition point. 

A description of the physical changes that occur during annealing. 

An informal discussion of the limiting factors on the annealing range is given in this blog. 

A description of the effects of attempting to anneal at the upper part of the annealing range. 

A description of why annealing at higher temperatures is counter productive. 

Bullseye used to publish three different annealing temperatures for transparent, opalescent, and gold bearing colours and gave an average of these to be the annealing temperature. This was before they began conducting research on annealing of thick slabs. As a result, they were able to determine annealing in the lower portion of the range produces good anneals with reductions in time spent in cooling.

A description of the annealing range and the advantages of low temperature annealing is given in this blog post. 

Although written to counter the mistaken view that CoE can determine the annealing temperature, this blog indicates that the annealing temperature is a choice within a range of temperatures. It also connects annealing soaks with cooling rates. 

The general point is that the annealing soak can occur at any point between the softening point at the top and the strain point at the low part of the temperature range. There are good reasons to avoid annealing above the annealing point (Tg). There are also good reasons to anneal near the strain point of the glass – saving time, electricity, and producing a denser glass. Annealing is critical, but the temperature at which you do it is less so.

 

All this has provoked me. There is so much more to say. So, I have begun a writing an eBook on Annealing – Concepts, Principles and Practice.  In the meantime, more information is given in the eBook Low Temperature Kilnforming

The Sol-Gel Manufacturing Process

 

The Sol-Gel Manufacturing Process

Posted on Jul 22, 2020

Sol-gel processes can be used to produce various high-performance solids including glasses and ceramics. In the world of glass production, sol-gel techniques offer a low-temperature alternative to traditional melt-quenching and thus save energy. These techniques can be used to produce an ever-growing group of materials with incredibly broad applications. Glasses produced via sol-gel routes can be highly pure and exhibit a range of other useful properties.

In this article, we take a look at how the sol-gel process was developed, how it works, and the properties of glasses produced in this way.

What is the Sol-Gel Process?

The sol-gel process is a manufacturing method in which bulk solid materials are produced from a solution of small particles. The process begins with the preparation of a solution of inorganic monomers, such as metal alkoxides and acetylacetonates; a hydrolysis agent, e.g. water; a solvent, e.g. alcohol; and an acid or base catalyst.1 The dissolved monomers undergo hydrolysis and polycondensation reactions to form a sol: a colloidal suspension of polymers or fine particles.

Further reactions form cross-links between the particles, solidifying them into a wet gel, which still contains water and solvents. Removing the water and solvents leaves a dry gel, one of the final possible products of the process. Further drying and heat treatment removes residual liquid and induces further polycondensation reactions, which can ultimately produce densified ceramics or glasses with novel properties.

Development of Sol-Gel Techniques

Sol-gel processes were first developed in the 1960s, with the purpose of producing bulk glasses at low temperatures, below 1000 C.2,3 These techniques contrasted greatly with conventional energy-intensive melting methods, which generally involve temperatures over 1400 C in furnaces.4 Years later, the rising popularity of optical fibers stimulated research into the production of silica glass preforms, from which optical glass fibers are drawn, via the sol-gel method.5

Producing silicate glass in bulk, e.g. rods and plates with dimensions exceeding tens of millimeters, was initially difficult due to the formation of cracks during the drying process. However, by the late 1990s, bulk silicate glass could be reliably and efficiently produced via a number of sol-gel routes. Alongside this research, efforts to produce more exotic multicomponent glasses, such as silicon oxycarbide glass, via sol-gel routes were proving successful, and enabling new glass compositions that could not be achieved with melt-quenching.6

Today, a huge range of multicomponent glasses and glass ceramics can be produced using sol-gel techniques, as well as more conventional silicate glasses.

Advantages and Properties of Sol-Gel Glasses

For similar chemical compositions, the overall structure and properties of sol-gel glasses are similar to those of conventional melt-formed glasses.4 Because of the high costs of specialized processing and raw materials for sol-gel approaches, they are not widely used for commercial production of ordinary silicate glass panels or containers. Instead, sol-gel techniques enable the production of specialized glass products which can’t be made using conventional techniques.

Low process temperature is one of the defining characteristics of the sol-gel approach, yet it is capable of producing a vast range of high-performance materials. When it comes to glass production, advantages over conventional melting include better homogeneity, better purity, and less energy-intensive production, although cost can still remain high. Critically, sol-gel techniques enable the creation of new materials with properties outside the range of conventionally made glass. These include useful electronic, optical, biomedical, mechanical and thermal properties that lend sol-gel glasses to a huge range of applications.

Applications of Sol-Gel Glasses

Some of the main applications of these materials are electronics, optics, thermal insulation, catalysis, and various mechanical and biological functions.

Electronics

Electronic components that can be produced using sol-gel glasses include capacitors and piezoelectric transducers.7,8 Novel applications of sol-gel glasses in this field include lithium-ion batteries and electrolytic membranes in fuel cells.

Optics

Sol-gel glasses can exhibit a range of useful optical and photonic properties. Often the sol-gel approach is used to deposit a glassy material in a thin film, where it has applications from colored coatings for car windows to laser elements, optical sensors and photovoltaics.9

Chemistry

Sol-gel techniques can produce materials with highly porous structures and very large internal surface areas. This lends them well to applications in catalysis, where the porous surfaces act as catalyst or catalyst-carrier. Such materials and applications include porous silica for chromatographic separation, and silicate-based catalysts for the production of H2. 10,11

Biosciences

Due to the high surface area and the easily controlled size and distribution of pores in sol-gel glasses, it’s possible to trap biological molecules or living tissues in porous glasses using sol-gel techniques. These high purity and homogeneous materials can be used for biomedical research and have been applied to the development of biosensors and tissue engineering techniques.12

The breadth of achievable properties of sol-gel glasses means that the range of possible applications for this class of materials is rapidly growing. As research continues, sol-gel glasses are redefining the way that we think about glass.

References and Further Reading

1. Sakka, S. Handbook of sol-gel science and technology : processing, characterization, and applications. (Kluwer Academic Publishers, 2005).
2. ROY, R. Gel Route to Homogeneous Glass Preparation. J. Am. Ceram. Soc. 52, 344–344 (1969).
3. Dislich, H. New Routes to Multicomponent Oxide Glasses. Angew. Chemie Int. Ed. English 10, 363–370 (1971).
4. Mackenzie, J. D. Glasses from melts and glasses from gels, a comparison. J. Non. Cryst. Solids 48, 1–10 (1982).
5. Sakka, S. Fibers from gels and their applications. in Glass Integrated Optics and Optical Fiber Devices: A Critical Review 10275, 1027507 (SPIE, 1994).
6. Pantano, C. G., Singh, A. K. & Zhang, H. Silicon oxycarbide glasses. J. Sol-Gel Sci. Technol. 14, 7–25 (1999).
7. Hatono, H., Ito, T. & Matsumura, A. Application of BaTiO3 film deposited by aerosol deposition to decoupling capacitor. Japanese J. Appl. Physics, Part 1 Regul. Pap. Short Notes Rev. Pap. 46, 6915–6919 (2007).
8. Tsurumi, T., Ozawa, S. & Wada, S. Preparation of PZT thick films by an interfacial polymerization method. in Journal of Sol-Gel Science and Technology 26, 1037–1040 (Springer, 2003).
9. Yoneda, T., Yasuhiro, S. & Morimoto, T. Sol–Gel Coatings Applied to Automotive Windows. in Handbook of Sol-Gel Science and Technology 1–15 (Springer International Publishing, 2016). doi:10.1007/978-3-319-19454-7_84-1
10. Lubda, D., Cabrera, K., Nakanishi, K. & Minakuchi, H. SOL-GEL PRODUCTS NEWS Monolithic HPLC Silica Columns. Journal of Sol-Gel Science and Technology 23, (2002).
11. Gronchi, P., Kaddouri, A., Centola, P. & Del Rosso, R. Synthesis of nickel supported catalysts for hydrogen production by sol-gel method. in Journal of Sol-Gel Science and Technology 26, 843–846 (Springer, 2003).
12. Baino, F., Fiume, E., Miola, M. & Verné, E. Bioactive sol-gel glasses: Processing, properties, and applications. Int. J. Appl. Ceram. Technol. 15, 841–860 (2018).

Preventing dog boning

Firing a single layer, even with decorative elements on top, is most likely to “dog bone” due to lack of volume.  With a single layer you are always going to have difficulties with volume control. 

Photo credit: Paul Tarlow

Unless you are satisfied with an angular tack fuse at the lower end of the tack fusing range, you will always run the risk of dog boning. All the other variations of tack fusing use increased temperatures causing the glass to begin to pull in along the long sides to a greater or lesser extent (more with contour fuse, less with angular tack fuse).

Dog boning occurs because as the glass softens and the edges begin to round, the viscosity takes over from the solid phase of glass as a major force.  Viscosity can be thought of as an approximation of surface tension. 

Glass is a material with a plastic range over several hundred degrees.  This means that the hotter the glass becomes, the less stiff it becomes, and the viscosity force thickens the glass toward 6-7mm in the kilnforming temperature range. The greater the temperature, the more the glass pulls into a ball shape, or in the case of sheets, thickens at the edges and thins in the middle.  Higher temperatures reduce the viscosity to the extent that it becomes as thin as one millimetre.

Trick the glass

To avoid dog boning on tack and full fusing, you have to trick the glass with some special scheduling.

The trick employs the concept of heat work.  The nature of glass allows you to put a lot of heat work into a piece by soaking for a long time at a low temperature.  You might think of it as a kind of sintering.

A description of sintering:

The atoms in the [glass] diffuse across the boundaries of the particles, fusing the particles together and creating one solid piece. [This can be done by heat at low temperatures with extended soaks.]  Examples of pressure-driven sintering are the compacting of snowfall to a glacier, or the forming of a hard snowball by pressing loose snow together.   https://en.wikipedia.org/wiki/Sintering

By sintering (sometimes called fuse to stick) or - in kilnforming terms - by the use of heat work you can achieve the result you want without dog boning.

By taking the temperature slowly to about 700°C to 720°C and soaking there for two to four hours you can achieve a rounded tack fuse without dog boning.  You will have to experiment with the exact temperature and length of soak to get exactly what you want.

The length of soak time or exact temperature is not vital.  The two in combination will achieve the effect you want.  The importance of observation of your firing is re-enforced in the cases of sintering.  You cannot be sure until you check during the firing whether the edges of the glass are rounded enough for your purpose. That observation will also tell you whether a slightly raised temperature would be useful.  You will learn the time required to achieve the effect by recording the soak time when you advance to the anneal soak and cool.

Further information is available in the ebook Low Temperature Kiln Forming.

By the use of heat work in kilnforming you can achieve tack fused pieces without dog boning.