Enlargement without Maths

 Setting out an enlargement grid can be done without the mathematics of ratios.  It uses an old method of estimated interval size and angles relating to the ends of the estimation and the width of the design.  This gives the method in simple images.

     Start with your original design

Draw line at a shallow angle from one corner

Determine number of grid lines (say 10) along the bottom edge.  Choose a length approximately the size needed for the grid.  Mark out the number of divisions with dividers or compass on that slope.

Connect the final mark with the corner at the end of the line started on.  Place a right angle on that line.

   Fix a long straight edge under that right angle and fix it so it does not move

·        Transfer the marks on the sloped line to the edge of the image.

This gives ten equal divisions. Adjust the divider opening to the width of the division.

Use dividers with this opening to transfer the division size to the other edge.

Do this on all four edges if a rectangle.

Do the same process for the enlarged size.

Draw a slope

Estimate the size of the division.  Mark that estimate on the slope as for the original design.  Fix a right angle between the end of the slope marks and the corner of the design.  Fix the straight edge and mark off the divisions on the enlarged size.  Transfer these divisions with the new division opening of the dividers

Draw the grid.

Note where the design crosses the grid lines. Transfer marks onto the enlarged grid proportionally.  To avoid confusion, mark one line in at a time.

An intersection of the design line two thirds up the design grid vertical gets a mark two thirds up the corresponding enlarged vertical.  The same with horizontal grid lines.  Connect the dots one line at a time in pencil.  They can be altered later and erased once the final lines are inked in.

 

Enlarging Designs by Hand

Not everyone has easy access to enlarging copiers.  Even when they are available, large enlargement ratios produce distortions.  This presents a dilemma when a big enlargement is needed.  Is it necessary to redraw the whole design at a larger scale?  There is a way to enlarge a design without machines or needing to redraw the whole.  This is a description of how it can be done.

The old fashioned way to enlarge an image is to grid the smaller original.  This grid is normally made in squares of convenient size.  The grid size does not have to fit evenly into the dimensions of the original.  It is easier if the longest side has a size of grid that fits evenly into it.  This probably means there will be an uneven fit of the square grid on the other dimension.  This is not a big problem. 

The size of the grid is related to the amount of detail.  More detailed original images need smaller squares than images with less detail.  Detailed images may require a 1cm/0.375” square grid or less.  This is to ensure all the detail is included in the enlarged image.  A less detailed original may only need a 2.5cm/1.0” grid.

Also, bigger enlargements require more squares on the original than smaller enlargements.  If you are enlarging more than three times, you should be looking toward smaller squares for the grid.  This allows you to maintain the curves and angles more easily on the enlarged copy.  Smaller enlargements can have a larger grid size.  The relevance of the grid size becomes apparent when you set out the enlarged grid.

It is useful to use a set of dividers to ensure the repeated grid size is set out on the boundaries of the original image size.  Once set, the distance between the two points of the dividers remains constant as you “walk” them along the boundaries.  If you mark all four sides of the image with the dividers, you only need a straight edge to draw the grid lines.  I draw the lines in pencil. Then if I make any mistakes, I can erase the lines and set new ones.

On another piece of paper set out the new enlarged size boundaries.  If you have set the boundaries at the correct size relative to the original, the new grid should fit evenly into the long dimension.  Multiply the grid size on the original by the enlargement ratio.  This gives you the size of the enlargement grid.  Set your dividers to this and mark off the enlarged grid.

In fact, most of the time, the difference between the final enlarged and the original size determines the enlargement ratio.  To get this ratio, divide the enlarged size by the original size to get the ratio.  This ratio needs to be applied to the new grid size.  If it does not fit well, adjust the dividers to the required size and mark the length again.

Example:

·        The approved design is 10 by 15cm/ 4” by 6”

·        The final size is to be 60 by 91.5cm/ 24” by 36” (assuming your design is in the same proportions as the final size).

·        Assuming your design is of moderate detail, squares of 1cm/ 0.39” might be enough to capture the detail.  For more detail, smaller squares would be required.

·        To determine the size of the squares in the full size design, divide the final size by the design size.  I prefer to use the bottom side for this calculation, but either side will work. The bottom side of the full size is 60cm, and the design is 10cm. The division shows that the squares on the full size need to be in a ratio of 1:6.0. This means the squares on the full size need to be 6.0cm/ 2.4”.

·        If this appears to be too large a grid, the squares can be divided to capture more detail.

 

The next blog post will show how to divide the design and full size without using maths at all.

Having marked the edges of the design with the grid sizes, draw the grid across the design.  Do this in pencil, so the grid lines can be erased when the enlargement is completed. This will give intersections between the design lines and both the grids. 

Enlarging involves marking these intersections on the full size grid in proportional locations.  E.g., if on the design the intersection on the grid line is 2/3 up the grid square.  On the large one mark it also 2/3 up on the corresponding square. Do one line at a time to avoid confusion.  When as much of the line intersections as you want for that element are transferred, draw the line in on the full size.  There will need to be some adjustment when finished, so use a pencil for all these operations.

When satisfied with the look of the full size, ink in the lines and erase the grid and any unwanted lines. You now have a full size cartoon to work with. 

Manually enlarging a design is most useful when you do not have access to machines, and when the enlargement is more than two times.  Machines distort the lines at high magnifications and require checking and often redrawing of edges and various elements anyway.

Is there a best separator?

 Is there a best separator?

Kilnforming separators

Separators for kiln forming come in various forms. Chemicals, liquids, sprays, refractory fibre paper, kiln wash, and others I suppose. Which is best?  Each separator has its uses. No one is useful in all circumstances.  Some will be best for one circumstance and others for another.

Boron nitride

Boron nitride (BN) is a high temperature lubricant. It can be sprayed or brushed onto the mould. It adheres to smooth non-absorbent surfaces.  BN is among the most expensive of separators for glass. It seems most useful on detailed, texture and casting moulds. BN is often recommended for steel moulds as it adheres to it better than kiln wash.  Although kiln wash will work as a separator on steel, boron nitride is easier to apply.  Various conditions apply to its use. 

Kiln wash

Kiln wash works well on slightly absorbent surfaces – ceramic moulds, and shelves, for example. It is the least expensive form of separator.  It is shipped as a powder to which five parts water is added to one of the powder.  This makes a liquid that can be applied to any appropriate surface.  It can be sprayed or brushed. The mix can be with less water on very absorbent surfaces, showing some of its flexibility. 

Almost all kiln washes contain kaolin which helps keep the alumina hydrate in suspension.  But most importantly, allows the solution to be applied evenly.  However, the same kaolin also slowly changes to a crystalline substance by 900ºC/ 1650º that sticks to glass. It needs to be re-applied after every full fuse.

Refractory fibre paper

Shelf paper works well on flat surfaces and simple moulds.  It is a moderately priced separator.  Two of the popular trade names are Papyros and Thinfire.  They both contain alumina hydrate but with different binders.  They provide a smooth surface for the shelf and cylindrical shapes. They are not so good at separating glass from irregular surfaces and incised details.  The shelf paper disintegrates after firing. Although it can sometimes be used several times if undisturbed.  The resulting powder is an irritant and should be disposed of carefully.

There are thicker refractory fibre papers.  These normally range from 0.5mm to 6mm.  Thicker versions are called blanket.  These have the same characteristics as shelf papers, although coarser.  They also do not use binders to keep them together.  These are most useful in forming moulds and insulating glass from rapid temperature changes.

 

The general statement is that there is not one separator that is best in all circumstances.  Each has its strengths.  Knowledge of the objective of the firing and its conditions will help in choosing the right one.

Kiln wash

People seem to avoid kiln wash. Some reasons are:

• It is messy.
• It requires effort to renew. 
• It needs drying between coats.
• It needs drying before firing anything on it.  
• It has lots of visible brush marks. 
• It must be renewed frequently.  
• It is dangerous.

These notes are to clarify some misconceptions about kiln wash use. Kiln wash is an economical glass separator that requires a little effort to use, but is effective and has less health risks than other separators.  Kiln wash is a separator, not a series of layers built up thickly. Some characteristics to consider in its use.

Thickly applied kiln wash on a mould

The Mix

You mix the powder with water.  Use a thin mix - 1:5 by volume.  There are various descriptions of the thickness of the mix.  Adhering to the 1:5 mix will ensure the right runniness of it.  The mix must be frequently agitated to keep the kiln wash in suspension while you are applying it.  If you do not ensure all the kiln wash is in suspension, you will not be applying enough separator.

Application

Use a soft bristled brush such as a hake or broad squirrel brush to let kiln wash mix flow onto the shelf or mould.  Hold the brush almost vertically and allow the kiln wash to flow off the brush while only lightly touching the shelf with the bristles.  Apply four thin layers in all directions – up/down, horizontal, and the two diagonals - to ensure coverage. 

Gentle application of kiln wash with a hake brush

Drying

No drying between coats is advisable or necessary.  The addition of a wet coat over the dry will wet the previous layer(s) and will lead to clumping.  It is not like painting wooden table that requires drying between coats.  For kiln wash all the coats should be applied without any drying between the directions of brushing.  View this as applying one coat.  And that is all that is needed.

Once the surface has a dull look, it is ready to use, even though not thoroughly dry.  At this stage, or later, you can remove any brush marks.  Place a sheet of paper over the kiln wash.  Smooth it by moving the paper with the palm of your hand over the surface.  Gently remove any dust.

Firing a newly kiln washed shelf or mould with the glass on top will dry the kiln wash before glass is soft enough to stick to it.

Removal

It is advisable to remove the kiln wash once it has been fired to full fuse.  The kaolin in the kiln wash becomes increasingly crystalline as the temperature rises. It is fully crystalline at about 900ºC/1650ºF. At the first full fuse it does not stick to transparent, but often to some opalescent glass. On the second full fuse the kiln wash sticks to all the glass.  At tack fuse temperatures, the kaolin has not fully crystallised, and several firings can be achieved without difficulty.  Experience will show how many firings - at your tack fuse temperature – are possible.

Re-coating

Painting over used dry kiln wash has the same difficulty of clumping as when initially applying.  It is also easier to remove kiln wash that has been fired only a few times. Kiln wash fired to full fuse several times requires much more effort than one fired to full fuse once.

Safety

Kiln wash contains alumina hydrate and most commonly kaolin. The powdered forms of these are irritants, not health hazards.  It is advisable to protect yourself and your work area.  Wear a dust mask when removing the dry kiln wash.  Do this is a well ventilated area or outside to reduce the dust in your studio. Dispose of the used kiln wash in sealed bags to avoid spreading the dust during refuse operations.

Fibre Paper Re-use in Kiln Carving

“I would like to use 1/4 inch Fiberfrax to impart texture on the back of transparent glass.  Is there a way to make it reusable?  I tried mould hardener on a small piece of it, but the hardener wasn’t absorbed.  I’m afraid the fiberfrax will lose its structure if I pre-fire it (to burn out the binders) before removing it to apply hardener.”

 

It is difficult to reuse refractory fibre paper after moving it between firings, but not impossible.  I have used two processes. One is to place the glass over the cut fibre paper. This works for small pieces. The fibre paper was placed on thinfire to allow air migration out. I used a long low temperature bubble squeeze to ensure the binder was completely burned out.

The other arrangement I have used for larger pieces.  This is to assemble and fire the fibre paper to burn out binders.  There is a large chance that not enough air will get to the centre of the fibre paper when large glass is placed on top.  Binder not burned out leaves a brown mark on the fibre paper and stains the glass grey. Turn off the kiln once all the binder is burned out as evidenced by the paper returning to white.  As soon as the temperature in the kiln is comfortable, you can place glass on top of the fibre paper.  It is strong enough that it will not be compacted by the weight of the glass.

Using un-hardened fibre

But there is no logical reason for these processes, although they work. Firing to about 500ºC/930ºF with a suitably long soak will clear those gasses before the forming of the glass begins.  You will know when there no longer is a smell of burning paper, or on more recent fibres a chemical smell.  Make sure you vent the kiln during this burnout to allow the smoke to escape.  For a large area, a soak there may need to be hours long.  Another check is when the fibre has turned white again, the binders are gone.  A further protection against bubbles in any area is to place the whole assembly on a bed of fibre paper.

It is possible to use un-hardened refractory fibre without a separator, as the older versions do not stick to glass easily.  However, if you are using the current eco fibres, they will stick in many areas.  Kiln washing any fibre before firing is the best protection against lengthy clean ups.  It also allows the best chance to remove the un-rigidised fibre for re-use.

A smoother surface can be given to the refractory fibre, if you want. Do this by smoothing powdered kiln wash over the bed layer and any other layers the glass will be touching.  An alternative to powdered kiln wash is to put Thinfire or Papyros cut to shape over each layer.

After firing, slide the fibre onto cardboard or another flat stiff surface. Then place into a large pizza or similar box. I have stored fibre in such a way for several firings.

Using hardened fibre

Of course, the fibre can be hardened by use of colloidal silica.  Make up the whole stack of fibre paper for the kiln carving.  Harden the whole stack at once. This helps to bind the layers together.  Brush on the hardener to the exposed part of each layer.  Cover both horizontal and vertical surfaces. Hardener does take time to soak into the fibre paper.  Give it time.  You can add more hardener at intervals.  Be careful to avoid overdoing it.  Fully wet fibre is difficult to move and takes a long time to dry - days.  The objective is to harden the surface of the fibre, not to harden the whole by soaking it.

Allow the carrier of the hardener to evaporate for hours or a day.  When you can move the fibre, fire to at least mid-700’s ºC/ 1300ºF to 1400ºF.  After firing, it must be covered with significant amounts of kiln wash. This can be as a liquid or as powder. I prefer liquid.  The kiln wash is required over all edges and surfaces to keep the glass from sticking to the fibre.

Storage of the rigidised fibre paper can be in the same way as for the fibre without binders or hardener.

Home Made Billets

You can make your own billets from small pot melts.  But why should anyone go to the effort? Some reasons are:

• ·        You can make your own colour. 
• ·        You can use your cullet/scrap (avoiding buying or making frit).
• ·        You don’t have to buy and break billet to size 
• ·        You can reduce the clouding caused by many microscopic bubbles surrounding the frit pieces. 
• ·        You can make a size to fit your casting mould. 
• ·        Potentially, you will reduce needling.

 Now you are convinced of the advantages, you want to know how.

Preparation

• ·        Select the glass. Avoid iridised glass and any ground edges – they will cause haze in the final casting. Wash all the glass. Place the glass in a small flowerpot.
• ·        Weigh out the amount of glass cullet needed for the mould and add about 50gms to account for the glass that will stick to the pot.  Calculating the required weight is relatively simple and this post gives the information.

Dams

• ·        Arrange dams in such a way that the resulting billet will fit into the mould without overhang.  It might be quite a tall billet. In which case cast it horizontal with the height as the length of the billet.
• ·        Line the dams with Thinfire/Papyros at least. One mm fibre paper would be better. 
• ·        The dams can be on a kiln washed shelf or on fibre paper. The bottom of the glass will be fine either way.
• ·        Place the pot above the dams.  The higher, the fewer bubbles in the billet.  And any left in the billet will be reduced by flow in the casting firing.
• ·        Multiple billets can be made of different colours, sizes, etc., at the same time.

Firing

• ·        Fire to around 900ºC/1650ºF and soak for hours.  Observation will show when the pot is empty.  Clue: There will be no string of glass from the bottom of the pot.
• ·        Anneal as for the smallest dimension.  If you are doing multiple sizes, the dimension must be taken from the biggest piece.
• ·        When cool, remove and clean the separator off the pieces thoroughly.  A 15 minute soak in a 5% citric acid solution will speed the process.

Casting

• ·        Place billet in casting mould. The first ramp rate needs to be for the smallest dimension of the billet.  This may be a slower rate than when using frit for casting.
• ·        Do a long bubble squeeze in the 650ºC to 670ºC range – up to two hours, but a minimum of one.
• ·        Fire to your normal top temperature and time.
• ·        Anneal for the largest piece.

 

More information here 

Kilnforming Opalescent Stained Glass

The statement that a sheet of glass can be fused to itself is true in certain circumstances.  It applies to transparent and some streaky glasses best.  These forms of glass are more likely to fuse together successfully although not formulated for fusing.

Transparent and Streaky Glasses

Of course, the best practice is to test for compatibility.  I found in my early days of sticking stained glass together that it was beneficial to test. In doing so, I found Spectrum and Armstrong transparent and streaky glass to be largely consistent across many sheets.  I did not have access to much Kokomo or Wissmach.  I cannot comment on how their glass behaves in terms of compatibility across the production range.  Not all transparent and streaky glass remains stable at fusing temperatures. There are some glasses that opalise, some change colour, some devitrify. This variability makes compatibility testing important - even for the transparent form of stained glass.

Photo credit: Lead and Light

Wispy Glasses

The statement about fusing to itself is less applicable to wispy glass.  Not all the wispy stained glass from the same sheet can be fused.  It seems to be dependent on the amount of opalescence in any one area of the glass.  I found that it is possible - if you are very careful - to fuse certain Spectrum wispies with the clear fusing standard on top, but not on the bottom.  This should be applicable to other manufacturers’ wispy glass too.  There must be a marginal compatibility that is contained by the clear fusing glass on top, but I am not certain.

Photo credit: Lead and Light

Opalescent Glasses

The statement about fusing to itself is almost completely inapplicable to opalescent glass.  Stained glass opalescent glass does not have the compatibility requirements of fusing glasses.  They very often severely devitrify when taken to fusing temperatures.  This devitrification means that opalescent stained glass is often not compatible with itself.  So, no amount of twiddling with schedules will make stained glass opalescent glass fusible, even with itself.

Manufacturers have spent a lot of time and effort to produce fusing compatible opalescent glass.  It is as though there is a minor element of devitrification embodied in the opalising process.  Whether this is so, it becomes very apparent on doing compatibility testing that opalescent stained glass has severe devitrification at fusing temperatures.

Stock photo

Compatibility Testing

It is important to test for compatibility before committing to the main firing.  Some transparent and streaky glass changes colour, devitrifies, and some opalise at fusing temperatures. This applies with even more force to wispies.  They contain a significant proportion of opalescence within them.  Some opalescents are so unstable at fusing temperatures that the devitrification becomes so bad the glass crumbles.

The importance of testing pieces of the sheet for compatibility before committing to a firing is reinforced by these factors.

Slumping

Slumping temperatures are not so high as fusing, and it is often stated that single layers can be slumped.  Again, it is not always true.

Some glasses change colour at slumping temperatures.  A few opalise. It is not always certain what effect moderate temperatures will have on stained glass.  The compatibility testing will show.  Observe the test firing at slumping temperatures.  Also, you will learn if there are changes at moderate temperatures.

One element must be commented upon about slumping.  It is important to have the edges finished to the appearance that you want the final piece to have.  The regularity of the edges without bumps or divots, and the degree of polish need to be showing before the firing starts.  The slumping temperatures are not high enough to alter the shape or appearance of the edges.

Firing of stained glass to itself is normally a low risk activity, but with unpredictable results.  It can teach a lot about behaviour of glass at higher temperatures.  Slumping single layer pieces can give information about the way single layers of glass slump or drape.  But testing is important for fusing.  And can inform about how the glass will react at slumping temperatures too.

Testing your Scoring pressure

 Most often people are asked to listen to the sound of scoring.  Unfortunately, different glass styles make different sounds. Float glass makes a particular sound, transparent stained glass makes a slightly different one, and opalescent glass makes almost no sound. Consistent pressure of the right amount is important to the clean breaking of glass. Therefore, we must learn to cut with the same consistent pressure on all types of glass, rather than listening for sound.

It is easy to tell when the scoring is too heavy.  A white line shows along the score.

The heavy score line near the break shows the white line and the irregular break

It is not so easy to tell if the score is too light or just right.

A heavy score in the distance and a lighter score nearer

Pressure

The general recommendations for the pressure to use during scoring is 4.5 – 7 Lbs or 2 – 3 Kg. This is difficult to judge. I found that I needed a means of letting people know for themselves the pressure they were exerting. It is not enough to watch and say that was too hard, that was too soft, etc.

My method of teaching novices how to judge the pressure they are using is to use a digital kitchen scale that can have the scale set to zero. Place a piece of glass no larger than the platform on top of the scales. Zero the scale display.  Have someone watch the scale display while you score in your usual way. Of course, you must not touch the glass with your other hand. Have them tell you the maximum and minimum weights displayed. Keep repeating until you can consistently use that 4.5 – 6.5 pounds (2 - 3Kg) pressure.

The testing setup showing a heavy score on the right and the start of a 1.9kg score on the left.

Consistency

The other important element of scoring is to keep the pressure consistent throughout the score. This test will also show how evenly you apply the pressure during the score. The objective of scoring is to use the correct pressure throughout the length of the score. If your pressure varies significantly during the score, it will be difficult to get the glass to break consistently along the score line. Because the amount of weakness in the surface created by the score is variable.

Your observer can tell you when the pressure is less than optimum or more than desired.  If the pressure variation has a reasonably consistent place in scoring - such as at the beginning, or on a curve - you can fix it. Concentrate on correcting the fall off in pressure. For example, most people start off with a lighter pressure than further into the score.  Getting the feel of the correct pressure will enable you to apply it right from the start of the score. Sometimes, people increase the scoring pressure when they come to curves. This test will show if that is true for you.

This curve was scored with 4.3kg pressure showing that heavy pressure can result in break outs from the score line

This testing can take quite a while. But it is worth the time spent in getting the scoring pressure right to reduce the number of unwanted breaks. However, it is not a one-time test. When I begin to have difficulties in breaking glass, I go back to this test to check whether I am scoring too heavily. In my scoring practice, I find that my best ones are those with 1.8 to 2.5kg (4.0 to 5.5 pounds) with the cutter I use.  This is less than many, but it has worked well for me for years.

There are, of course, other elements that go to making a good score and break. But the most important thing in scoring and breaking opalescent glass is to avoid too heavy a score by listening for a sound. Cut to a consistent pressure whatever sound is heard.

 

Heat Up vs Annealing

I am amazed by the effort put into ramp up rates, bubble squeezes, and top temperatures in comparison to annealing.  The emphasis on social media groups seems to be to get the right ramp rates for tack fuses and slumps, bubble squeezes, etc.  Most of the attention is on the way up to processing temperature.

The treatment of annealing and cooling is almost cavalier by comparison.  The attention seems to be on what temperature, and how long a soak is needed.  Then some arbitrary rate is used to cool to 370ºC/700ºF.

Annealing, in comparison to firing to top temperature, is both more complex and more vital to getting sound, lasting projects completed.  Skimping on annealing is an unsound practice leading to a lot of post-firing difficulties.

Annealing is more than a temperature and a time.  It is also the cooling to avoid inducing temporary stress. That stress during cooling can be large enough to break the glass.  This temporary stress is due to expansion differentials within the glass.

People often cite the saving of electricity as the reason for turning off at 370ºC/700ºF.  My response is that if the kiln is cooling off slower than the rate set, there will be no electricity used.  No electricity demands.  No controller intervention.  No relay operation.

Annealing at the lower end of the range with a three-stage cooling provides good results.  The results of Bullseye research on annealing are shown in their chart for annealing thick items.  It applies to glass 6mm and much larger.  It results from a recommendation to anneal at the lower end of the annealing range to get good anneals.  Other industrial research shows annealing in the lower end gives denser glass, and by implication, more robust glass.  Wissmach have accepted the results of Bullseye research and now recommend 482ºC/900ºF as the annealing temperature for their W96.  The annealing point of course remains at 516ºC/960ºF.

Bullseye research goes on to show that a progressive cooling gives the best results.  They recommend a three-stage cooling process.  The first is for the initial 55ºC/º100F below the annealing temperature, a second 55ºC/100ºF cooling and a final cooling to room temperature.

It is a good practice to schedule all three cooling rates.  It may be considered unnecessary because your kiln cools slower than the chart indicates.  Well, that is fine until you get into tack and contour fusing.  Then you will need the three-stage cooling process as you will be annealing for thicknesses up to 2.5 times actual height.

 

Of course, you can find out all the reasons for careful annealing in my book "Annealing; concepts, principles, practice" Available from Bullseye at

https://classes.bullseyeglass.com/ebooks/ebook-annealing-concepts-principles-practice.html

Or on Etsy in the VerrierStudio shop

https://www.etsy.com/uk/listing/1290856355/annealing-concepts-principles-practice?click_key=d86e32604406a8450fd73c6aabb4af58385cd9bc%3A1290856355&click_sum=9a81876e&ref=shop_home_active_4