Mica

What it is

Mica is widely distributed throughout the world and occurs in igneous, metamorphic and sedimentary rocks. Mica is similar to granite in its crystalline composition.  The nearly perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagonal sheet-like arrangement of its atoms.

Mica can be composed of a variety of minerals giving various colours and transparency. Purple, rosy, silver and grey colours come from the mineral called lepidolite.  

Dark green, brown and black come from biotite.  

Yellowish-brown, green and white come from phlogopite.  

Colourless and transparent micas are called muscovite.  

All these have a pearly vitreous lustre.

The melting point of mica depends on its exact composition, but ranges from 700⁰C to 1000⁰C.

Glass has a specific gravity of about 2.5, and mica ranges from 2.8-3.1, so it is slightly heavier than glass.

Tips on uses of mica powder and flakes

The naturally occurring colours are largely impervious to kiln forming temperatures.  Other added colours have various resistances to the heat of fusing. This is determined by the temperatures used to apply the colour to the mica.  Cosmetic mica is coloured at low temperatures and will not survive kiln forming with their colour in tact.

Mica does not combine with glass, but is encased by glass as it sinks into the glass surface.  You can use various fluxes to soften the surface of the glass.  Borax is one of those.  The cleaving of the mica results in only the layer in contact with the glass sticking.  The upper layers brush off.  This applies to both powder and flakes. One solution is to fire with mica on top in the initial firing and then cap for the final one.

When encasing mica exercise caution. Micas flakes must be applied thinly, as air is easily trapped between layers which leads to large bubbles from between layers of glass.  This is the result of the shearing of layers of the flakes allowing air between layers.  Although powdered mica is less likely to create large bubbles, air bubbles are often created for the same reason.  This is the reason it is most often recommended to fire the mica on top. 

Of course, one use of the mica to make complicated designs is to cover the whole area and fuse.  Then sandblast a design removing the mica from areas of the glass. You can then fire polish, or cap and re-fire to seal the mica.

Mica safety

MSDS for mica only mentions the inhalation of the dust as a risk. Mica is resistant to acid attack and is largely inert.  Inhalation of the dust is a (low level) risk.  Any significant health and safety problems relate to the coloured coatings.

Deep slumps

One of Karl Harron's deep slumped bowls

Deep slumps require multiple stages to get even drops without thinning the sides.  There are several makers of staged slumping moulds which allow progressively deeper slumps in a series of firings into deeper moulds.

If you have a steep-sided mould, you will find slumping directly into the shape difficult.  There will be uneven slumps, thinning of sides, hang-ups, etc., among your attempts to achieve the slump in one firing.  It is possible to mimic this series of moulds without buying the whole set. 

To avoid these difficulties, you can build up the inside bottom of the mould by placing powdered kiln wash in the bottom and smoothing it to a gentle curve. You should aim for a gentle shape as in a ball mould. 

After the first firing, remove some of the powder, placing it in a clean container.  Shape the remaining powder into a deeper slump than the first one. 

It takes some time and practice to achieve a smooth even curve.  You can ease the shaping process by cutting the intermediate shapes from stiff card.  This can be rotated to achieve an even curve in the powder.  Remove any excess powder and do a final rotation to give the powder a final smoothing.  Place the glass back on the mould and fire.

It may be that you will need to repeat this several times to get the full slump.  Separate template curves need to be cut for each slump if you are doing more than one intermediate slump. It does depend on the steepness of the mould sides and the depth of the slump as to how many stages are required.  Sometimes the slump can be achieved in only two stages.

After firing the powder, pour it back into your kiln wash container, as it still is good for mixing to apply to shelves, moulds etc.

This method is useful for any mould that is too deep for achieving the slump in one firing, and without buying intermediate moulds.  Remember the final result will be smaller than the size of the deep mould, as the span of the glass becomes less with each deeper slump.

Effects of Annealing at the Top End of the Range

It is possible to begin your annealing at any point in the annealing range.

The annealing point is the temperature at which the glass most quickly relieves the stress within.  This occurs at the glass transition point. 

The  annealing range is between the softening point and the strain point of the glass.  No annealing can be achieved above the softening point, nor below the strain point.  This range, for practical purposes can be taken to be 55°C above and below the published annealing point.  For thick slabs, Bullseye has chosen to start the anneal 34°C below the published annealing point of 516°C.

High Annealing Point

They could have chosen to use a higher point, even up to 571°C, the approximate strain point of the glass.  The effect of this is an extended anneal cool.  The reasons are as follows.  

The anneal soak does not need to be extended, as the purpose is to get all the glass at the same temperature in preparation for the annealing cool. 

The cooling rate must be slower (approximately one third the rate) than an anneal soak at a lower temperature, as the glass must be maintained at the same temperature throughout the long cool.  

Also, the initial rate of cool needs to be maintained down to the strain point, which is 110°C below the softening point.  Of course, after that initial cool, the speed of cooling can be increased.

Low Annealing Point

Starting the anneal cool closer to the strain point requires a longer soak to ensure the glass is all at the same temperature (+/- 5°C) before the anneal cool begins.  Typically, this initial soak would be for an hour before the initial cool begins (for a 6mm to 9mm thick piece).

Effect of the Differences in Approach

The advantages and disadvantages centre around these needs to 

• soak long enough to get all the glass to the same temperature and secondly, to 
• cool slowly enough to maintain the even temperature distribution throughout the glass.

Example

If you think of an example of a piece of Bullseye glass 12mm thick, it will show the differences in approach.

High temperature soak

A soak of 30 minutes at 571°C (the highest possible start for an annealing soak) is required to even the temperature.  To ensure the temperature differentials in the glass do not deviate from the +/-5°C, the cool needs to be at 18°C per hour down to 461°C.  It is possible then to increase the speed to 36°C down to 370°C.  This gives you a total annealing cool of just over 5 hours.

Low temperature soak

Starting the anneal at 482°C requires an hour soak followed by a decrease in temperature of 55°C per hour to 427°C, and an increased rate of 110°C to 370°C.  This gives an anneal cool time of 3 hours and 30 minutes.

The example shows how, although the annealing result may be the same, there is considerable time saved (for thicker pieces) in using the lower part of the annealing range to begin the annealing.  It also will save some electricity.

However, an anneal of 30 minutes at 516°C with a cool of 80°C per hour to 370°C will still give a perfectly adequate anneal for 6mm thick pieces.

Breaks after the Piece is Cool

People sometimes fire a piece only to have it break after it is cool.  They decide to re-fire with additional decoration to conceal the break.  But it breaks again a day after it has cooled.  Their questions centre around thermal shock and annealing. They used the same CoE from different suppliers, so it must be one of these elements that caused the breakage.

Thermal Shock

This is an effect of a too rapid heat change.  This can occur on the way up in temperature or on the way down.  If it occurred on the way up to a fuse, the edges will be rounded.  If it occurred on the way up to a slump the edges may be sharp still, but the pieces will not fit together because the slump occurred before the slump.  It the break occurs on the way down the pieces will be sharp.  The break will be visible when you open the kiln.  More information is here.

If the break occurs after the piece is cool, it is not thermal shock.

If the break occurs some length of time after the piece is cool, it can be an annealing or a compatibility problem.  They are difficult to distinguish apart sometimes.

The annealing break usually crosses through the applied pieces and typically has a hook at each end of the break.  If the piece has significant differences in thicknesses, the break may follow the edge of the thicker pieces for some distance before it crosses it toward an edge. This kind of break makes it difficult to tell from an incompatibility break.

An incompatibility break may occur in the kiln, or it may occur days, months or years later.  Typically, the break or crack will be around the incompatible glass.  The break or crack may follow one edge of the incompatible glass before it jumps to an edge.  The greater the incompatibility, the more likely it is to break apart.  Smaller levels of incompatibility lead to fractures around the incompatible glass pieces, but not complete breaks.

There is more information about the diagnosis of the causes of cracks and breaks here.

Annealing

Another possible cause of delayed breakage is inadequate annealing.  Most guidelines on annealing assume a flat uniform thickness.  The popularity of tack fused elements, means these are inadequate guides on the annealing soak and annealing cool.  Tack fused items generally need double the temperature equalisation soak and half the annealing cool rate. This post gives information on how the annealing needs modification on tack fused items. 


Compatibility

The user indicated all the glass was of the same CoE.  This is not necessarily helpful. 

Coefficient of Linear Expansion (CoE) is measured between 0°C and 300°C. The amount of expansion over this temperature range is measured and averaged. The result is expressed as a fraction of a metre per degree Celsius. CoE90 means that the glass will expand 9 one-thousandths of a millimetre for each degree Celsius.  If this were to hold true for higher temperatures, the movement at 800C would be 7.2mm in length over the starting size.  However, the CoE rises with temperature in glass and is variable in different glasses, so this does not tell us how much the expansion at the annealing point will be.  It is the annealing point expansion rate that is more important.  More information is here.

Compatibility is much more than the rate of expansion of glass at any given temperature.  It involves the balance of the forces caused by viscosity and expansion rates around the annealing point.

Viscosity is probably the most important force in creating compatible glasses. There is information on viscosity here.  To make a range of compatible glass the forces of expansion and viscosity need to be balanced.  Each manufacturer will do this in subtly different ways.  Therefore, not all glass that is claimed by one manufacturer to compatible with another’s will be so. 

All is not lost.  It does not need to be left to chance.

Testing glass from different sources is required, as you can see from the above comments.  It is possible to test the compatibility of glass from different sources in your own kiln.  The test is based on the principle that glass compatible with a base sheet will be compatible with other glasses that are also compatible with that same base sheet.  There are several methods to do this testing, but this is the one I use, based on Shar Moorman’s methods.  

If you are investing considerable effort and expense in a piece which will use glass from different sources or manufacturers, and which is simply labelled CoE90, or CoE96, you need to use these tests before you start putting the glass together.  The more you deviate from one manufacturer’s glass in a piece, the more testing is vital. 

In the past, people found ways of combining glass that was not necessarily compatible, by different layering, various volume relationships, etc.  But the advent of manufacturers’ developing compatible lines of glass eliminated the need to do all that testing and experimenting.  While the fused glass market was small, there were only a few companies producing fusing glass.  When the market increased, the commercial environment led to others developing glass said to be compatible with one or other of the main producers of fusing compatible glass.

If you are buying by CoE you must test what you buy against what you have.

The discussion above shows that even with the best intentions, different manufacturers will have differences that may be small, but can be large enough to destroy your project.  This means that unless you are willing to do the testing, you should stick with one manufacturer of fusing compatible glass. 

Do not get sucked into the belief that CoE tells you anything important about compatibility.

Sticking Kiln Wash

Sometimes people experience kiln wash sticking to the bottom of their glass. 

You need some understanding of what kiln wash is to know why the wash sticks. It is largely due to the chemical changes in the kaolin at fusing temperatures.

Opalescent glass does tend to pick up kiln wash more easily than transparent, and does it more at higher temperatures. It is the case that at higher temperatures and longer soaks, the kiln wash is more likely to stick to any of the glasses than at lower temperatures and with shorter soaks. This re-enforces the mantra of "low and slow" to avoid problems in kiln forming.

To achieve the same effects at lower temperatures as at higher temperatures, your rate of advance needs to be slower from the slump point to the top temperature.  This additional heat work will achieve the desired effect with a lower temperature.

One kiln wash, Primo, does not contain china clay.  If you use this and it is sticking to the bottom of the glass, you may be firing too high. Try a lower temperature with a longer soak to reduce the kiln wash pickup. 

Multiple firings of kiln wash

Compatibility Tests

These procedures are based on the observation that glasses compatible with the base glass are compatible with each other. This means that you can test opaque colours’ compatibilities with each other by testing each of them on clear strips.

Annealing test

These tests must be combined with an annealing test.  This consists of putting two pieces from the same sheet of glass together - so you know they are compatible - and firing them along with your compatibility test.

Viewing the results of your annealing through the polarised filters shows whether there is stress left in your annealing.  If there is, the compatibility tests are inconlusive as there is no difference in appearance of stress whether from incompatibility or from inadequate annealing.  Once you have the annealing right, you can then interpret the compatibility tests done at the same time.

Strip test

Cut a strip of base glass 75mm/3" wide and as long as convenient for you or your kiln.

Cut clear glass squares of 25mm/1" to separate the colours.

Cut 25mm/1" squares of the colours to be tested.

Start with a clear square at one end of the clear strip and alternate colours and clear along the strip finishing with a clear square.

Place two strips 25mm/1" wide either side of the clear and coloured squares.

Add a stack of two layers of clear to the kiln before firing as a test for adequate annealing. If the annealing is inadequate, then the whole test is invalid.

In this test there is very mild stress showing from the dark brown and dark green.  This is well within the limits for compatibility.

Test the result with polarising filters. Start with the clear annealing test square. If no stress is apparent, go to the test strip. But if stress is apparent in the annealing test, look to your annealing schedule as something needs to change. Usually the requirement is a combination of a longer soak at the annealing temperature and a slower annealing cool.

To test for compatibility, look carefully for little bits of light in the clear glass surrounding the colour. These are indications of stress – the more light or the bigger the halo, the greater the stress. Really extreme stress appears to be similar to a rainbow, although without the full spectrum.

You can use this test to determine if you annealing is satisfactory for larger pieces. In this case you should use at least 100mm squares. Stack them to the height of your planned project and dam them with fibre board or other refractory materials to prevent spread. Fire to full fuse and anneal. When cool check for stresses.


The tile method looks at compressive factors too.

Cut a 100mm/4" square clear tile

Cut two strips of glass 25mm/1" wide and 100mm/4" long for each test

Cut two rectangles of 25mm by 50mm (1" by 2") of the same glass for the two remaining sides

Cut a square of 50mm/2" for the centre. The glass in the middle is normally the test glass. To be very certain of what has happened you can do the reverse lay up at the same time. You put coloured glass around the outside, but in this case the inside needs to be clear or transparent. At least one element needs to be transparent enough to view the stress patterns, if any. So you could have a clear middle and black exterior, and vice versa.

This test is a more time consuming process and you may wish to use it only for larger projects.

Also look at the use of polarising filters

Charges for Repairs

Repairs always cost more than the owner or artist expects on initial inspection.  The cost is very similar to, or more expensive than, the cost of a new panel if the whole has to be taken apart and renewed.

If it is a repair to part of the window or object, you need to be careful that you do not under price.  The cost elements you need to consider are these at minimum:

• Glass
• Materials
• Time
• Overheads
• Travel
• Installation
• Contingencies
• Profit

Glass - and the cost of obtaining it.  Can you obtain the same or very similar glass to the original?  If you can’t, is the client willing to have the repair in different glass?  If you get approval, you need to cost it – whether you already have it or not.  If you do not have it in your stocks, you need to add in the cost of getting it whether that is travel or postal order.  You need to include the time either or both methods involve in the costs.

Materials – The materials you will use in addition to the glass need to be considered.  These include solder, Foil or lead, flux, patina, cleaning materials, etc.

Time - labour and admin. You need to assess how much time it will take to do the repairs.  Then multiply that by your labour rate. You do have one, don’t you?  If not, get down to it and create one. Use steps one and two of this description.   You also need to take into consideration the time to recreate a pattern for the broken area if extensive.

Overheads – If your overheads are not included in your hourly rate, this is the time to include them in the pricing.

Travel = Your mileage rate + time to get there and back.  If you don’t have a mileage rate, look at what your local authority allows.  This will be lower than what businesses allow, but are reasonable, and publicly available.  (At the time of writing the allowance in Scotland is approximately £0.50 per mile.)  It takes time to get to the location, so this needs to be included in the cost too. Of course, if they are willing to bring the item, it reduces the cost to the client.

Installation – If you are expected to install the piece, you need to include travel (there and back at least twice) and time.  You also need to include the estimated time to remove and install a substitute (and its cost) as well as installation of the repaired piece.

Contingencies - All repairs have uncertainties.  You do not always know what the progress of repairing will reveal.  You can agree with the client that any work required in addition to the initial agreement will be notified for the client to decide whether to proceed or not.  However, you can take on the risk. This is what the contingency is for. You need to build allowance for these unforeseen developments.  A 10% to 20% of the total costs addition to the price is sensible if you are taking the risk.

These seven elements added together give you the cost of doing the repairs.  That is the bottom line.  But there is one more element to consider:

Profit – You do expect to get a profit from all this work, don’t you?  If not, why do the repair at all?  You are not a charity.  Of course, you can decide to give away your profit.  Before you do, think about what you have to pay for repairs – to your car, your plumbing, etc.  You deserve some profit on everything you have invested in this craft that you love.  The love will die without profit.

The profit level will depend on your objectives, but will range from 20% (very low) to 100% (what shops charge). If you put your work in a gallery or shop on a sale or return basis, you expect to have to pay at least 30% on the sale.  That should be the minimum basis of your profit level on any repair.



This may all sound like it is too much trouble for a simple repair.  Yes, it does take a bit of consideration to start with.  But once you have established the basic labour, travel, overhead and profit levels, the rest is pretty straight forward.  You will have an idea of how long it takes to do the work, to travel, the glass costs, etc., and the profit level. You only need to multiply by the rates you have established to give you the price.  I should warn you - it will be much higher than you initially thought.

CMC as a Medium

There is a lot of use of powdered glass in a medium supplied in an applicator bottle.  This is convenient and expensive.  You can approach the consistency of the commercial product by use of CMC

CMC is carbyl methyl cellulose. It is a binder (glue) and it helps keep solids suspended in liquid. You can buy it at a pottery supplier as it is often used in glaze mixtures and known as a glaze binder. It is also used a lot in the food processing industry and is available as food grade CMC.  It normally is supplied in powder form.

To make use of it you need to dissolve a teaspoon or two in a half pint of water and let it stand. It does take a while to wet and in doing so it expands. By the next day it will be a thick mass. It can be further diluted, but it is often best to make it to the consistency you will need for the current purpose.  It will require a little experimentation to get the proportions right for various purposes.  

Put on a dust mask. Sift the powdered glass to remove the coarsest particles and mix the result with the CMC, 1 to 2 of powder or more.  Mix thoroughly and leave to stand overnight. Then dilute to the desired flow if required and mix well. Again let it stand overnight to completely incorporate the powder.  If it is too liquid, it is desirable to add more powder than more CMC to avoid diluting the colour.

Channels in Jewellery Items

The principle in forming channels in fused glass is to keep the space open with something that will survive the firing and can be easily removed.

You can use kiln washed wire, mandrels, or tooth picks which you can pull out after cooling. These tend to leave a residue of the kiln wash behind. So this is best used on opaque items.

You can use rolled or cut fibre paper, which can be washed out after cooling, leaving a clean hole. This is works well on transparent items.

Both these methods tend to leave bumps over the channel. So you can make a three layer piece. Cut the middle layer short enough to allow the element to keep the hole open (toothpick, cut piece of fibre paper, wire etc.) to be placed with enough overlap of the top layer to catch the bottom layer. In this kind of setup you need to make the top layer a bit longer than the bottom layer. Make sure you are generous in the length of the "hole keeper" so if the glass (now possibly 9mm) does expand you do not trap the material inside.

Of course on a three layer set up like this you could use thin glass which would give you about 6mm of thickness thus eliminating the spread due to volume. In this case you would need to use fibre paper or wire that is about 1.5mm high/thick. It is probably best to have a thin piece of glass on each side of the “hole keeper” to ensure the glass does not retreat due to lack of volume.

You can experiment with a layer of standard and two of thin in various combinations to find the one you like best.

Removing Bubbles

Inclusions and Bubbles

The inclusion of material between two or more sheets of glass has the risk of creating bubbles.  The size of these often relate to the size of the inclusion.  The inclusion can be glass (powders, frits, cut pieces), mica, metals, foils, etc.

The important element in eliminating bubbles is to have a long slow bubble squeeze from the bottom of the forming temperature to the top slumping temperature.  If this is combined with supports at the edges or a fine film of clear powder, it will help reduce the interior bubbles to a minimum.  The supports at the edges may be as small as fine frit (and some use powder over the whole surface).

But, once you have bubbles in the piece, what can you do?

You can drill a hole in the bubbles, or break the bubbles and fuse again, but there will be distortions visible in the resulting piece.

Another method to reduce the effect of bubbles, is to flip the piece and fire upside down to drive the bubbles to the bottom of the piece.  Be careful to use low fusing temperatures to avoid enlarging the bubble.  At the finish, the bubble will still be in the glass but will not be protruding above the top surface.

It may also be possible to combine the two processes.  Drill a small hole in the bubbles and fire upside down.  If you do this you need to place the glass on porous fibre paper, not just Thinfire or Papyrus, to allow the air to be compressed out of the bubbles.  You also need to allow a significant amount of time around the slumping temperature for this to happen.

Once you have fired upside down, you will need to fire polish the surface again. Do not despair at multiple firings.  A lot of people fire their pieces many times to achieve the effects desired.

Make Your Own Stopping Knife

“Stopping knife” is a traditional term for an oyster knife with a weighted end.  This makes it a multi-purpose tool that manipulate glass, dress lead came, act as a fid, act as a putty knife, and become a hammer.  It also stands up on its own.  I find it the single most useful too in leaded glass panel construction.

This note is how to get from here:

To here:

The process relies on the low melting temperature of lead.  This means that you can use stiff paper wrapped around the handle of the knife to contain the molten lead until it cools.

First you set the oyster knife into a vice and cut two dovetail joints at right angles to each other into the end of the wood handle.  This will insure the lead is firmly grasped by the wood and will not come loose during use.

I do this with a fine bladed saw such as a hacksaw, coping saw or even a dovetail saw.  There are Japanese saws that work very well too, but are not so widely available.

The top of the dovetail joint should be just a millimetre or two off centre. 

The angle should be about 30 degrees from vertical.  Saw down far enough to get a 6mm chisel into the space between the two angled cuts.

Chisel out the wood between the cuts.

Repeat for the second dovetail at right angles to the first.

Now you are ready to prepare the oyster knife to become the stopping knife.

Use paper of more than 90 grams per square metre, such as cartridge paper to form the narrow cone.  Set the knife at a slight angle on the paper. 

Secure the beginning edge to the knife handle with a bit of masking tape.  Mark the paper 5 mm – 10 mm above the top of the handle.  This will be the fill indicator when pouring the lead.  If you over-fill the cone, the stopping knife will be heavy and uncomfortable to use.

Roll the paper around the handle to form the cone.  This cone should be as close to vertical as possible.  A wide based cone will, of course, provide stability, but it will add so much weight as to be uncomfortable to use.  It will also be so wide as be uncomfortable for the palm of your hand.

You can unwrap the paper and start over if the cone becomes too wide.  The key is to start the wrapping just before the handle begins to taper toward the end of the handle.  The other way of looking at it is to attach the paper just as the expanding taper stops.

Try to keep the paper cone as smooth as possible.  This will form the shape of the lead end of the handle.  You want it to be as circular as possible without dents or angles.

Now you are ready for the casting.

I use a small old cast iron pot to melt the lead.  I place this over a camping gas burner to provide the heat.  I promise that I did straighten the stabilising legs before lighting the camping burner.

Put some old lead came into the pot to be melted.  While this is coming up to heat, place your wrapped oyster knife in a vice with heat resisting materials around the site to catch any spills.

Put sufficient lead into the pot, as there will be impurities floating on top and the lead will cool quickly when taken off the heat.  The photo below shows the amount of lead used.  This 100mm diameter pot has lead barely covering the bottom.  You do need enough lead to complete the pour at one go, as a second pouring will not stick to the first adequately.

The photo shows the last piece of came just about to be melted.  This is the time to begin the pour.  If the lead is too hot, it burns the wood creating gases and multiple bubbles splashing hot lead and leaving an unpleasant surface for the tool.  As the last piece of the came melts and leaves its impression as the piece on the left, it is time to pour.

Pour at a steady rate into the paper cone until you reach the height indicator you previously marked in the paper.  When you stop pouring, set the pot on a heat proof surface.  You will notice some smoke and browning of the paper.  That is normal.  This picture shows the effect of the hot lead on the paper once the smoking has finished.

This photo shows the inside of the cone while cooling.  The cooling process will take about an hour.  You will be able to check, by touching the paper, how hot the whole is. 

When the whole is cool, you can unwrap the paper from the handle.

This shows the roughness of the handle end.  This is due to the bubbling from the scorching of the wood and paper.

When the paper is removed and the lead is fully at room temperature you can use a rough file to remove the bubbling and to round the edge of the lead.

The oyster knife has been transformed into a stopping knife and is ready to use.

Borax solutions

A borax solution can act as a devitrification spray. That is its usual application in kiln forming.  But it can be used in other ways too.

Borax is a flux helping to reduce the firing temperature of glass. So, it can be used as a medium for powdered mica which can be painted or sprayed onto the glass. It also helps reduce the oxidisation of included metals.

Obtain borax that has no additives. Put a couple of teaspoons into water and bring to a simmer. Remove from the heat and cool. Decant the almost clear liquid off the sediment and you have a saturated solution of borax ready to use. 

If you are really parsimonious, you can add water to the crystals remaining in the pot and heat to get another saturated solution. You could do this until there was no residue, but that would get tedious.

Add a couple of drops of washing up liquid to the solution. This is enough to break the solution's surface tension. It helps to give an even distribution of the solution across the clean glass by reducing the beading of the liquid that otherwise occurs.

You can paint the solution onto the material - glass or metal - with a soft brush such as a hake brush, or you can spray it on with a pump spray container.  Be careful to clean the spray container immediately, as borax crystals form quickly.

Permanance 

Description of devitrification
Temperature range

Characteristics