Wednesday, 20 March 2019

Kiln wash

When considering how many layers of kiln wash to put on shelves, especially in melts, combing and other high temperature operations, you need to remember what the kiln wash is doing – what its purpose is. 

Kiln and batt wash, shelf and mould primer are all different terms for the same thing – a separator between the glass and the kiln furniture or mould.  The amount needed is enough to completely cover the shelf. This is usually 4 coats - one top to bottom, one side to side, one each diagonal.  If you are spraying the kiln wash, use a coloured kiln wash to help ensure coverage. The shelf is adequately covered when the shelf is a uniform colour although a sense of the original remains while the kiln wash is wet.  Additional coats do not provide additional protection. The disadvantage of thick coatings of kiln wash is that the excess tends to stick to the glass as it is lifted from the shelf or mould.

This post gives guidance about the methods for application of kiln wash.

Wednesday, 13 March 2019

Textured Side

There is a little concern about whether the textured side of the glass pieces in leaded and copper foiled glass should be towards the inside or outside.

The traditional advice is to have the textured side toward the inside.  This is based on the piece being used as a window. It is easier to keep the weather side clean if the smooth side is on the outside. The same thinking leads to the recommendation to allow the cemented panel to rest with the smooth (outside) down.  This minimises the thickness of the putty and so allows less water to collect on the outside horizontal leads.

If the window is not primary glazing, it does not matter which side, nor how consistent you are in placing the glass.  It becomes a matter of aesthetics – which ever way you prefer is fine if it gives you the effect you want.

There is a small visual effect if you are using transparent glass.  There is slightly more dispersion of light if the textured side is outwards. 

Placing the textured side inwards can be useful if you wish to indicate a rough surface contrasting with a smoother one.

These considerations show that the placing of the textured side is largely determined by the function of the panel and the aesthetics applied.

Wednesday, 6 March 2019


The successful application of patina to solder or zinc depends on an understanding of what patina is, how it works and the methods of applying it.

What is it?


Patina is a thin layer that variously forms on the surface of copper, bronze and similar metals (tarnish produced by oxidation or other chemical processes), or certain wooden furniture (a sheen produced by age, wear, and polishing), or any similar acquired change of a surface through age and exposure.
The chemical process by which a patina forms or is deliberately induced is called patination, and a work of art coated by a patina is said to be patinated.
The word "patina" comes from the Latin for "shallow dish". Figuratively, patina can refer to any fading, darkening or other signs of age, which are felt to be natural or unavoidable (or both).

A description of patination and the industrial process:

“In their natural state, most metals combine with chemicals in the earth or air to create metallic compounds that change their surface colour, which appear as rust or tarnish. These thin layers of corrosion are nature's patinas.”

“Among the most common procedures [to patinate] are immersion and spraying. During immersion, a piece is cleaned with sandblasting or chemicals, then dipped into a prepared liquid compound, creating an immediate change in colour. Alternatively, a piece is sprayed or brushed with a patina solution, allowed to air dry, and spritzed again. This oxidation process creates corrosion on the metal's surface that forms a layer of patina. Other methods include heat, dabbing and wiping, anodizing, and random contact patina.”

Source: Triple-S Chemical Products

A product – Black on Solder – is described and the industrial process illustrated:

“DESCRIPTION: Black on Solder is a chemical formula developed to achieve a black antique finish on Tin/Lead or Solder areas (60-40 or 50-50). This solution is a non-chromate, non-cyanide liquid solution widely used on lighting fixtures, tin wares, sculptures, gift items and other decorations. The surface will not chip, flake or peel.

“PREPARATION: Parts must be free of grease, alkalinity or acid when Black on Solder is applied. Parts must be thoroughly cleaned and deoxidized prior to blackening. … Do not use petroleum degreasing solvents that leave a residue on the surface. Rinse thoroughly with over flowing cold water to remove residual cleaners and dust. It is important that alkaline cleaners are completely rinsed off prior to blackening.

“IMPORTANT: Triple- S does NOT recommend using any sort of alcohol, solvent, acid or degreaser to clean parts prior to solution application. … Powdered cleaners such as Ajax or Comet can also be used. Use the cleaner in conjunction with a scotch brite pad and apply medium strength scrubbing to prepare the part then thoroughly rinse with fresh water. ….

“APPLICATION: Clean the part with [your chosen material]. Rinse thoroughly with water and dry. Apply [the patina] solution with a brush or spray evenly and let it react. Rinse with water and air dry or wipe with a cloth to dry the surface. [Repeat this as necessary.] It is recommended to protect the finish with a clear [varnish]”

Source: Triple-S Chemical Products

Take note:

The above quote is from a company that works with metals exclusively and is an illustration of how important cleaning is for good results in patina application.  When cleaning in proximity or on glass different processes must be used to protect the glass.

1. I never would use abrasive or corrosive materials to clean solder lines holding glass.  The most aggressive cleaner I use is that intended for fibreglass baths.
2. I never use abrasive methods in conjunction with painted glass.
3. Do not use metal or scouring pads when cleaning
4. I never use patina on any part of a panel that has painting on any of the glass. The acid will remove or damage the painting.
5. I never use patina on leaded panels at all.

I suggest these precautions should always be followed.

These sources indicate that a patina solution is used to form a thin layer of corrosion to the material.  To do this, the metal must be cleaned of oils, and be acidically neutral.  Cleaning is to be done with household cleaners such as powdered or cream cleaners applied with moderate pressure by synthetic scrubbing materials such as a dish scrubbing pad (sometimes called a green scrubby). The metal then needs application of running water (not a bath of water) to rinse off any residues. 

The clean metal needs to be dried before application of the patination solution.  Apply with a brush or sponge, or spray and allow time for the patina to react with the metal.  Rinse with water and allow to air dry.  If wanted, the drying can be aided by wiping with a soft cloth or absorbent paper.  Often a second or third application is required to achieve the depth of colour desired.

You can then apply a varnish or wax to shine and protect the colour of the patination.  This protective process must not involve scrubbing, as that will remove the patination layer from the metal.

Do it Yourself Colourations

Goran Budija has listed a wide variety of patination formulas and methods in his publication.  What follows is a reworking of his data.

Patination of Tin

Black 1
Immerse objects in heated solution(70C). When colour is developed rinse well, dry and wax.
5 gms Bismuth nitrate
50cc Nitric Acid
80gms Tartaric acid
1 litre water

Black 2
Immerse objects in the hot (70C) solution.
30gms Ammonium chloride
7.5gms Molybdenum acid
1 litre water

Greyish black
Immerse objects in the room temperature solution.
200gms Iron III chloride
1 litre water

Bronze brown
Dissolve ingredients in water acidified with nitric or hydrochloric acid. Apply to the surface(s).
3 gms Ammonium chloride
12gms copper acetate
20ml vinegar
500ml water

Bronze colour.
Mix diluted solution of copper sulphate and cream of tartar, Rub it on an object.
Formula: equal parts of:
Copper sulphate
Potassium hydrogentartarate/cream of tartar

Patination of Zinc

Black. 1
Ingredients must be dissolved in hot water, then filtered and used.  Immerse objects and take them out immediately. Colour develops after contact with air.  Repeat if needed, rinse well and dry.
125gms copper sulphate
60gms potassium chlorate
1 litre water

Black. 2
Immerse objects in heated solution (90 C).
12gms copper sulphate
15gms potassium permanganate
1 litre water

Black. 3
Immerse objects in the solution. (room temperature)
20gms ammonium molybdate
5gms sodium acetate or sodium thiosulphate
1 litre water

Greyish black.
Immerse objects in the solution (approximately 20 minutes).
200gms Iron III chloride
1 Litre water
Collection of formulas for the chemical, electrochemical and heat colouring of metals, the cyanide free immersion plating and electroplating, by Goran Budija.  March 2011.  Zagreb, Croatia

Summary of applicable DIY formulas and methods

Goran Budija recommends hot application to get a black patination, but this is not usually suitable for stained glass work.  Cold application will also work but needs more time and repeated applications to have the same effect as hot immersion.  Whether you choose Black 1 or 2 will depend largely on the availability of the chemicals.

A cold method of patination is the Greyish Black using iron III chloride, which is easily available. More applications and drying will intensify the colour.

To get a bronze patination of solder equal parts of copper sulphate and cream of tartar made into a paste and rubbed onto the solder will be effective, although not a copper colour.

Black 1 seems the most useful method and formula for zinc framing of stained glass panels.  It is a cold application and immersion can be substituted by painting or brushing on the chemical solution.  Note the multiple applications required to get the depth of colour required, and the thorough cleaning and rinsing noted in the industrial process.

Wednesday, 27 February 2019

High Fast Slumps

What are the possible effects of fast rises to a high temperature for a slump?

Some of the possible effects of fast rises to a relatively high temperature slump are these:

Uneven slumps can occur. 
·         This largely due to differential heating of thicker/thinner parts. 
·         It can also emphasise anything off level.
·         Any unevenness in the heat across the kiln can also be emphasised by the rapid rise in temperature.

Uneven slumps can be promoted by contrasting colours. Dark and light colours heat at different rates, leading to one area of the glass slumping before another.

A dark/light contrast can lead to stress fractures in fast firings.

In a fast firing the top heats faster than bottom leading to the possibility of splits on the bottom of the piece

The edges of the piece heat faster than centre, increasing the possibility of spikes at the edge.

Fast slumps require higher temperatures to achieve the slump.  This means there will be more marking of the bottom surface.  It often includes stretch marks especially at the rim.

The Alternative to Fast High Temperature Slumps

Slow and Low

Slow rises in temperature means the slumps can be done at lower temperatures. Lower temperatures usually mean more control and fewer marks from the mould.  It does mean that you will need to observe at intervals to get the soak time you need, but this is required for all variations in rates and layups, as well as new moulds.

Wednesday, 20 February 2019

Combining Black and White

Black and white are at almost opposite ends of the viscosity spectrum in glass terms. Black is the runniest, and white is the stiffest. Black transmits heat more quickly to the lower layers than white.  White is the glass that absorbs and transmits heat most slowly.

an example from Pintrest

A lot of care is required when combining the two.

If the white is on top of black, the white shades the heat – more than other colours - from the black underneath, so a lot of stress can build up in the black.

You need to give a lot of time for the two to adjust to each other. A slower rate of advance than normal is advisable. A significantly longer soak at annealing temperature is required. The annealing cool needs to be much slower than for other glass of the same dimensions.  Consider slowing the rates to half your normal firing rates.  Also double your soak times.  After some experience you will be able to alter these cautious rates to those more suitable for you.

Wednesday, 13 February 2019


Kilnformers seem keen to reinvent terminology and then wonder about imprecise language being used in the field. Much of the terminology for kilnforming is already available from ceramics. It makes sense to continue to use that terminology where it applies.

A soak at a stated temperature is the same as "hold" at the same temperature.

The concept of soak is more useful than the term “hold”.  “Soak” implies the temperature is held at temperature to allow the heat to soak into the glass. And that is the purpose of a hold.  Using the term “soak” brings this purpose into the thinking about scheduling.  It is related to the concept of heat work

Using the concept of heat work allows you to use a slow rise to a temperature for a short time to get the effect you want.  Or to rise to a temperature in the normal way but with a long soak.

This is how you can get a tack fuse at 750C with a long soak – say 30 mins - as at higher temperature for a shorter soak – say 780C for 5 minutes. This the concept of heat work in practice.

Wednesday, 6 February 2019


Lamination in kiln forming is the adhering the glass pieces together without changing the shape of the glass.  On a laminated piece the edges of the glass will still be sharp but cannot be pulled apart.  Each manufacturer's glass will have slightly different lamination temperatures and it will be affected by the length of soak.

How do I find the lamination temperature?


Make your chosen layup in clear glass.

Peek at your glass at frequent intervals from 550C.  The rate of advance should be slow, say 150C or less. When it is observed the edges are beginning to round, you know you have the high-profile tack temperature for that rate of advance.

On another firing of the same setup and rate of advance, soak at 20C lower than the previous temperature for 60 mins. You need to keep peeking during the soak to ensure the edges remain sharp. 

When you see the edges begin to round, you need to advance to the cool and record the length of the soak used.  You will need to shorten that soak by the interval of your peeking.  If you were peeking every 10 minutes, reduce the length of the actual soak given by 10 minutes for the next firing.

These three firings will give you a schedule for laminating glass together for your chosen layup.  Other layups will require slight variations which will require observation to determine how much change from the original schedule is required.

Anneal and cool carefully

Do not forget to schedule the anneal soak and cool for at least twice longer than for a tack fuse each time.  This may make the soak four or more times longer than for a full fuse.

The reasons for the longer soak and slower cool are:
·         The glass pieces are not incorporated with each other. 
·         The pieces will react to cooling in different ways. 
·         Different colours have different viscosities and different contraction rates.
·         The shading effect of one piece on top of another is intensified. 

All these factors make it important to ensure all the glass is at the same temperature (the anneal soak) and that the pieces, that make up the whole, cool at the same rate even when shaded.

Wednesday, 30 January 2019

Scheduling for Size or for Thickness

When scheduling a firing, which is most important, size or thickness?

As usual in kilnforming - it depends.

Generally, the thickness is the most important consideration.  The concept is that the heat needs to be put into and released from the glass through its thickness as it is larger than it is thick.  This means the shortest distance for the heat to travel is through the thickness.

But, if the pieces are small, the heat can be released from the sides too. In this case, size is important.  Small pieces, say under 100mm, can be fired quickly.

If the piece is very large relative to your kiln, you need to slow the heating and cooling as the hotter and cooler areas of your kiln will be brought into consideration. Large pieces are those that occupy almost the whole of your kiln. This is especially important in side fired kilns but has application in top fired kilns.  The heat is uneven in all kilns to some extent.  To overcome the limitations caused by this, you need to slow the rates.

The general rule
But, in general, you fire for the thickness of the piece (as determined l factors such as uneven thicknesses, tack fusing, stress points, etc.) because that is the important variable for absorbing and releasing heat.

Always consider whether things needing different firing conditions should be fired together or in separate firings.  This applies to slumping as well as the fusing of pieces.

Wednesday, 23 January 2019

Melts, Apertures and Height Effects

The effects on the pattern of melts are a combination of several factors. The normal pattern is of spirals as a thread of glass moves down to the shelf and begins to spiral just as any other viscous fluid around the high spot of the drip.  The specific effects centre around three main elements.

Aperture size
The size of the holes determines the diameter of the thread of flowing glass.  Also, the larger the diameter, the quicker the flow.

relatively small apertures
large, long apertures

Height from shelf
The height from the shelf has the effect of determining both the thickness of the thread at touch down and the degree of spiralling.

Relatively low screen

Relatively high screen

The temperature and time determine the heat work.  The amount of heat (as well as top temperature) influence the flow of the glass.

These three elements interact

Aperture size determines the maximum diameter of the thread.  You can thin the threads by having smaller grids or holes. 

The height affects two things. 

Height affects the relative thickness of the flowing thread. Higher makes for thinner strands. The reduction in size can be lessened by placing the apertures closer to the shelf.

Height also affects how the thread behaves on touching the shelf.  More spiralling occurs with height.  A low height will reduce the spiralling to just moving outwards.

Note that when talking about height, it is relative to the aperture sizes.

Heat affects how the glass flows
The higher the heat or the greater the heat work, the faster the glass flows.  Lower heat gives slow moving threads.  Faster flowing glass promotes thicker threads.  Slower moving threads can take up patterns other than spirals.

These factors give you three interacting elements

You could have, for example, a high screen with large openings and low heat to give thin threads with eccentric spiralling.

You could have low height with small apertures and high heat to give thick threads with minimum spiralling.

In theory, you could have at least twelve main combinations by using the extremes of each element, with multiple variations of dimensions in each case.

Experimentation Required

This is to illustrate the interactions are complex and require significant experimentation to be able to predict the probable outcome.  The outcomes will always be only probable, even though you can come to control more aspects of the process and you develop experience.

Wednesday, 16 January 2019

Diagnosis of Slump Breaks

The diagnosis of breaks in slumps is a little more difficult than in full fuses. In full fuses sharp edges to the break indicate the fracture occurred on the way down in temperature and rounded edges indicate the break happened on the way up.

But the temperatures in slumping are not high enough (in normal slumping procedures) to round no matter when the break occurred.  If the break occurred on the way up, it will remain sharp, just as it would if it broke on the way down.  There needs to be another way to diagnose when it broke.

The key is to try to fit the pieces back together. 

If the break occurred on the way up, the pieces will separate to some degree – depending on the force of the stresses.  After this break the glass will slump into the mould from their separate places.  When cooled and you attempt to put them together they will not fit perfectly.

If the break occurred on the way down, the whole piece had already slumped as one.  The broken pieces will fit together, as the slump broke apart after the form was achieved.

Wednesday, 9 January 2019


This post is not about the materials that go into the making of glass, but about ways of forming glass once melted or dripped into a space.

Formers are a bit different from moulds.  They are more like the formers used in concrete structures – they are there to resist the movement of the contained materials and give the form or shape desired rather than a natural flow.

These formers can be of anything that can resist the firing temperatures of the process.  Some of the materials are stainless steel, ceramics, fibre board and paper, vermiculite, kiln brick, and I am sure there are others.

Refractory Fibre
Most of these require a separator between themselves and the glass.  The ones which do not are untreated refractory fibre board and fibre paper. 

Most paper is not sufficiently strong to stand on its own. Instead it is used flat and the shape cut out of it.  It can be made in several layers and pinned together to achieve the height desired.  It should be lined in the interior with a thin fibre paper to avoid seeing the layers of the former in the edge of the glass.

For thicker work, fibre board can be used with the shape or form cut from it. Alternatively, it can be used on its side backed up by kiln brick or other material to resist movement. More information on methods and safety are here

If hardened, refractory board and paper will need separators between glass and former, just as most other materials will.

Sometimes the fibre board and fibre paper are not heavy enough to resist the flow of the glass.  You can use weights to help resist the movement.  At other times, the glass flows under the fibre and then you need something heavier.  Fortunately, there are a number of refractory materials that can be used.

Other common formers

Vermiculite board is another refractory material that can be cut and shaped much like fibre board.  The vermiculite needs to be covered with kiln wash where it might come into contact with glass or be lined with fibre paper or another separator.

Calcium silicate board can be used in much the same way.  It also needs a separator but does not stand up to such high temperatures as vermiculite.

Ceramics, especially in the form of cut up kiln shelves can be used as straight formers.  They have the advantage, over refractory fibre paper and boards, vermiculite and calcium silicate, of being heavy.  They can resist the movement of thick glass. They need to have a separator and usually a 3mm fibre paper, cut 3mm shorter than the final thickness of the piece, will provide the cushion in the movement that the glass needs.

Kiln brick is an often forgotten former.  The bricks can be cut and formed in many ways, even if not so freely as fibre board and paper.  The bricks do need fibre paper separators to keep the glass from getting into the pores of the brick.

Stainless steel is a common former too.  These are usually formed into an already determined shape and so are not so adaptable as many of the other formers.  Steel contracts much more than glass and needs a cushion of fibre paper, usually 3mm thick to avoid sticking to the glass.

More information on most of these formers can be found here.

Wednesday, 2 January 2019

Seedy base glass

Sometimes your clear base has bubbles, or as the trade calls it, seeds.  When capped with opalescent glass, in certain circumstances, these tiny bubbles can become larger and rise to the surface, pushing the opalescent aside as it rises.  This leaves a clear spot in the midst of the opalescence.

Clear cap
One way of reducing this problem, is to avoid it altogether.  This can be done by placing the clear on top of the opalescent as a cap.  This way the bubbles, if any, are rising through the clear.

Flip and Fire
If you can’t, for one reason or another, cap the piece with clear, you can fire upside down. Again, the bubbles are rising through the clear.  When the firing is complete, you can flip it over to the right side.  You will need to clean thoroughly and take to a fire polish temperature to get the shiny surface back.

Heat Work
Another way is to fire to a lower top temperature with a longer soak.  This means the glass can take up the profile you want without becoming so soft that the bubbles can rise through the glass.  You will need to observe to determine when the glass has the right profile, and then advance to the cooling and anneal phases.

Low and Slow
This last way of reducing the possibilities of bubbles rising through toward the top is based on the characteristics of glass.  As glass becomes hotter, it becomes less viscous and so allows the air to rise toward the top of the glass surface.  Using a low temperature gives a more viscous glass to resist the bubble movement.  The long soak at the chosen lower temperature allows the surface of the glass to take up the profile you want, as the surface is hotter than the bottom of the glass, therefore reducing the possibilities of bubbles rising.  It does take a longer soak at the top temperature, but it also reduces the marking on the bottom of the piece.

This low temperature process is using the principles of heat work.  The effect on the glass is a combination of temperature and time.  The higher the temperature, the less time is required.  The longer the time, the less heat is required.  The heat work put into the glass to achieve the effect you desire is determined by the combination of temperature and time used in firing the glass.  This principle of heat work is why you can achieve the same effect at very different temperatures, depending on the length of time a piece is soaked.