Effect of Combustion Gasses

Some materials will partially or completely combust at fusing temperatures. This gives off gasses which expand and blow big bubbles from under the glass.

Some kiln washes, especially for ceramics, give this problem. If you believe this is the cause, try a different brand of kiln wash or pre-fire the kiln shelf.

Sometimes organic materials have been introduced accidentally or purposely onto the shelf. Either clean the shelf of the old kiln wash, or support the glass on beads, or frit to allow the gasses to burn out before the glass slumps to trap the gasses.

Damaged Shelves

Shelves that have gouges or pits can give rise to bubbles from trapped air. Since air expands much more than glass, it will force its way out through the most plastic material. At fusing temperatures, this is the glass.

To determine if this is the problem, note where the bubbles form in relation to the shelf. If it is always in the same area, there is reason to believe it is related to the shelf. By noting the location you now have an area to inspect for damage.

If you can see no damage, it may be that the shelf is warped, or has a low spot. These can trap air, just as the pits and gouges can. But these are difficult to determine by direct visual inspection. You can place a straight edge on the shelf and look for any gap as you move the edge along the shelf.

Possible solutions are:
- Avoid fusing over the shelf "pits".
- Fill shelf scratches and nicks with kiln-wash.
- Mend the shelf with cement fondue or other refractory materials.
- Fire on fibre paper - this will provide an escape path for the air.
- Flip warped shelves, as the opposite side is likely to be equivalently bowed, but in the opposite direction. The degree of bowing is imperceptible, so will not affect the appearance of the fused result.
-Grind the shelves flat. This can be done commercially with a milling machine, or you can do it manually. Place two shelves with their concave faces together with some sandblast grit between. Rub the shelves together and this will reduce the convex areas on each to flat.

Bubbles Between the Glass and Shelf

Eliminating the bubbles that can occur between your kiln shelf and the glass is important because these are the bubbles that can rise up through your work, blowing a large hole through the entire piece – Australians call these space helmets.

Common causes relate to damaged shelves, firing too rapidly, uneven heating, and combustion gasses.

Bubbles Between Layers – “Flip and Fire”

Another approach to avoiding bubbles is to plan on two firings. This works well for pieces that have multiple layers, with glass or other inclusion in the middle.

For the first firing, put the middle pieces flat on the kiln shelf with one layer of glass on top. Take this to at least a tack fuse, although full fuse temperature is better as there should be no remaining gaps for air to be trapped within. Now turn this over and clean it well. Place this part in the kiln with the middle layer up. Place the top layer over this piece – now right side up – and take to the full fuse. Remember that now you are firing a thicker piece than in the first firing so take the temperature up more slowly.

This is most often applied to three layer pieces, but in principle can be applied to any number of layers.

Using baffles
Supporting the edges
Design elements
Arrangement of glass sheets

Bubbles Between Layers – Baffles

Bubbles are often caused by the edges of the layers sealing before the air can escape from between. This frequently happens in side fired kilns, and top and side fired kilns.

Set up heat baffles around the edges of the sheets being fused to decrease the chance of the edges getting more heat than the centre and trapping air between layers. The baffles can be made from kiln furniture, strips of fibre board, cut pieces of old kiln shelves, etc. - anything that will witstand the top temperature.

Arrangement of glass sheets
Designing for fewer bubbles
Edge supports to reduce bubbles

Bubbles Between Layers - Supports

A common way to reduce bubbles that appear between layers of glass is to support the edges of the glass allowing the middle of the top sheet to sag before the edges so pushing the air in front of the collapsing glass.

You can do this with small beads - especially useful for large glass sheets. These beads are prepared in advance by firing small pieces of glass during a previous fuse firing. The glass draws up into a bead-like structure. You place these beads around the edge of the glass sheets. Use glass that is the same colour as the base glass to avoid strong colour spots in the finished work.

Make sure you advance the temperature slowly enough to allow the glass to slump from the middle outwards, allowing the air to escape. Note that even clear beads will leave a trace, so design your work to take advantage of these faint marks.


Another method is to put small pieces of frit every few centimetres around the edge of the bottom piece of glass. Place the top piece of glass on top of these spacers. When fired, the middle of the top sheet will sag first and the area of contact between the two sheets will spread from the middle pushing the air out as it goes, just as with the beads. But the evidence is not so marked as with the use of beads. However the frit is not so useful on large pieces.

Design factors
Arrangement of layers
Using baffles

Fibre Papers

As there always is concern about the health effects of ceramic fibre paper, the report I prepared for a supplier may be of interest.  It can be found here.

Bubbles Between Layers - Design

Design your work to minimise the possibilities of trapped air.

One way to do this is to use strips. Lay thin strips of glass on edge and fuse these together, instead of layers stacked on each other.

Another is to design work with many smaller pieces, rather than large ones. These create more pathways for air to escape.

Some advocate cutting the bottom layer in several strips to allow the air exit spaces from between the glass layers.

Note that all these methods leave marks of where the edges of the cut glass was, so they need to be planned to fit with the design.

In general terms, you need to think about how the air will move out of the piece. Are there places where there is no escape for the air? Allow a channel for the air to move from the centre to the outside.

Glass arrangement considerations
Supports
Using baffles

Bubbles Between Layers - Arrangement

There are a variety of ways to minimise bubbles between layers.

You will have noted that there are smoother and rougher sides to the glass. Putting the two rough sides together will increase the number of small bubbles in the finished piece. But the opposite –smooth to smooth – does not produce the smallest bubbles. The fewest small bubbles are produced when one smooth side is touching the rough side of the other layer of glass. This “roughness” allows any air to find a way out. Smooth to smooth tends to produce fewer but much larger bubbles.

Design factors
Supports during the forming stage
Using baffles

Attaching a Spider to a Lamp

To get the maximum support from the spider, bend the legs to fit the shape of the lamp. Then clean the spider assembly well with steel wool, or if particularly dirty with fine sandpaper, until it is bright again.

Apply flux and run a film of solder onto the legs where they will be in contact with the lamp. This will give you an indication of the amount of heat required to solder the legs to the lamp. It will also make it easier to fix the legs to the lamp once the appropriate temperature has been achieved in the legs.

You need to use the full power of your soldering iron, as the brass soaks up a lot of heat. If your iron is small you may need to change to one with higher wattage for this work.

As the heat is transferred quickly to all parts of the spider, wear gloves or hold with pliers while soldering.

Hanging Panels from the Borders

The hanging method for copper foiled and leaded panels depends to a large extent on size and weight. The larger and heavier the panel is, the stronger support that is required. Smaller light weight panels are not usually a problem as the solder lines and joints can take the weight. Leaded panels require more support than copper foiled panels once they are over a few kilos, or are anything but rectangular.

For heavier panels you need to have stronger supports than just the perimeter calmes or solder beading.

For rectangular panels you can use a stronger edge came such as zinc or brass. Solder this to each meeting joint throughout the length of the panel. This distributes the hanging stress across the panel more effectively. Simple soldering at the four corners of the calme will rely on just those solder joints to carry the whole weight of the panel.

You need to make the vertical borders of single pieces so that you are not relying on the strength of a single solder joint at some point along the side. Although the joint may be strong enough at present, it must stand up to the weight of the panel over a long period of time.

All this relies on secure attachment of the hanging hooks or wire

Glass Weaving

In its essence, weaving is creating a series of strips with waves, moving alternate ones a half step along and inserting straight strips into the channels provided.

It can be as sophisticated as you can devise, but remains the shaping of a series of strips through which other, straight strips are threaded at right angles to the shaped ones. As in cloth weaving, there are a great many variations that can be devised.

You can use a variety of material to slump over – covered steel pipe, cut up kiln shelves, brick, fibre board, etc. - but you must remember that you will need at least 10mm height, as the upper and lower pieces of glass are 3mm each and the one inserted will also be 3mm, leaving only 1mm tolerance. You also need to ensure the material slumped over is far enough apart to accept the width of glass you will be threading through. If you are using 20mm strips, you probably will need at least 25mm intervals between the slumping strips. Make sure they are parallel as well as evenly spaced. You will need to soak at slumping temperature longer than for a simple shape, as you want the slump to be close to vertical.

When threaded, you can tack or full fuse the piece and subsequently slump it if desired. The amount of space between the “threads” will depend on the steepness of the slump. If the slump is too deep you will find the lines of the “threads” will be uneven and may even fold over one another.

So this is yet another area of kiln forming that is simple in principle, but requires a lot of experience to get a really good looking piece at the end.

Drilling Glass, 2

Using a Drill Press

It is best to have a drill press if you are doing a lot of drilling. It provides a stable drilling action and the pressure on the bit can be controlled.  It is important to ensure the bit is running true without wobble. The drill press should have instructions to help correct any untrue running of the chuck.  Make sure the drill bit is secured firmly.  Core drill bits are easier to keep true, as they normally have a threaded fixing.

With a drill press, you can drill continually until the hole is completed, or until a white paste or dust begins to appear. This indicates the drilling is being done dry and will in a few moments heat up the glass too much. When the white paste appears, back out of the bottom of the hole a little to allow water to flush the glass out. Then continue.

Keep a firm grip on the glass being drilled. Maintain its position, especially if you are intending to back off intermittently to allow water to the bottom of the hole. This enables you to get back into the hole without scratches.

If possible, submerge the piece. But if that isn’t possible, just squeeze a little puddle of water on the surface and watch it swirl around. You can see if it is pulling ground glass out of the hole by watching the circulation. Placing a plasticine or clay dam around the drill area will keep the water confined.

Don't push down any harder than you comfortably can with the tips of your fingers. Keep it steady. Listen for the sound of diamond grinding glass

If the core gets stuck in the bit, knock it out with some stiff wire or a nail. Always remove each core right after drilling. They are very difficult to remove if there is more than one in there.

Every diameter drill bit has an optimum drill speed. The smaller they are the faster the speed required. Based on what the manufacturers recommend, a Dremel running at top speed is way too fast. When using a Dremel for drilling glass, slow it down with the speed control. Drill presses do tend to be on the slow side for glass drilling so it takes a bit longer, but there are big advantages in other respects.

For other tips on glass drilling see:

Keeping things wet
Using a drill press
Drilling with a Flushing Head
Avoiding chipping
Drilling holes with copper tube and grit
Drilling tools
Drilling glass without a drill press
Hole Placement
Drilling speeds for diamond bits in glass

Keeping Wire Hangers in Place

Even though it is normal to place the wire between two layers of glass, it often moves from its original placing.

Using glue only keeps the wire in place while moving the piece(s) to the kiln. The glue will burn off at just under 500C, which is before the sticky point of glass, so it cannot hold the wire in place at the critical temperature – from about 700C. In fact, if you fire quickly the glue can “boil” and cause the wire to move.

There are a variety of methods to help keep the wire where you placed it. Some of them follow.

You can try weighting the wire down with small scraps of glass to keep the wire in place until the glass sticks to the wire. The scrap will often form a small bead that can be used in other projects. Sometimes though, the scrap sticks to the wire.


Another method is to place a small piece of 3mm fibre paper under the wire to support it during the firing. This will be enough to keep the wire from moving, and the scraps of fibre paper can be reused many times.


You could also bend the wire loop so that the end touches the shelf. The part in between the glass needs to be flat with the bend starting after the wire emerges from the glass. You can bend the wire straight after firing.


Flattening the wire by tapping the wire – placed on an anvil – with a hammer will reduce the possibilities of movement, and certainly any rolling possibilities. It will also have a greater area of contact with the glass.


You can also make a shallow groove in the glass where the wire is to go. This can be done with a Dremel type tool with a diamond bit, or on the small diameter bit on the top of a glass grinder.
Lay the glass in the groove and cap with the top piece.

Drilling Glass 1

Keeping Things Wet

It is important always to keep the drill bit and glass wet, otherwise the glass gets too hot and will break. There are a variety of things you can do to achieve this.

• Drill under water in a container
• Drill in a ring of clay, plasticine, etc., holding water. To do this, you need to make a ring about 50mm / two inches in diameter and press it around the drill site. Fill the ring with water and a little diamond coolant. This will cool the drill site and glass. Diamond coolant is not necessary, but extends the life of the bits.
• Use a recirculating water pump such as those made for indoor water features. Direct the small flow of water to the drilling site and catch the water in the bucket in which the pump is submerged.
• Use a glass drill with hollow core bits and an internal water feed. This is the most expensive but it is the best equipment with which to drill large holes.

For other tips on glass drilling see:
Keeping things wet
Using a drill press
Drilling with a Flushing Head
Avoiding chipping
Drilling holes with copper tube and grit
Drilling tools
Drilling glass without a drill press
Hole Placement
Drilling speeds for diamond bits in glass

Drilling Glass, 3

Drilling with a Flushing Head

A flushing head with a re-circulating pump will deliver water to the drill site through the core of the drill. These are supplied complete or as a fitting for an existing drill press. This is suitable for holes of 4mm and larger. Smaller core drills are impractical both because the glass is easily trapped in the drill and the wall thickness of the drill makes them almost solid anyway.

An additional requirement is to have a means to direct the water back to the reservoir.

Every diameter drill bit has an optimum drill speed. The smaller they are the faster the speed. Drill presses do tend to be on the slow side for glass drilling, but often have ways of altering the speed. So it takes a bit longer, but there are big advantages in other respects.

Don't push down any harder than you comfortably can with the tips of your fingers. Keep it steady. Listen for the sound of diamond grinding glass

If the core gets stuck in the bit, knock it out with some stiff wire or a nail. Be careful not to damage the edges of the drill bit. Always remove each core right after drilling. They are difficult to remove if there is more than one in the core of the bit.

For other tips on glass drilling see:


Keeping things wet
Using a drill press
Drilling with a Flushing Head
Avoiding chipping
Drilling holes with copper tube and grit
Drilling tools
Drilling glass without a drill press
Hole Placement
Drilling speeds for diamond bits in glass

Drilling Glass, 4

Avoiding Chipping

There are a number of methods to avoid chipping out the back of the glass when drilling:

• Placing a piece of scrap glass under your good glass will help avoid chipping on the backside. By pressing firmly but gently on the glass (not the bit) the bit will go through the upper piece of glass without chipping the back. This can be a difficult process to keep stable when both the pieces of glass are wet.
• Another method is to put duct tape under the glass to help minimise chip out.
  Drill from both sides to avoid chip out as the bit breaks through. Go slowly toward the bottom of the hole. When the hole is almost through, turn the glass over and drill back to front.
• Sometimes the glass is curved and drilling from the back is not easy. This is when the drill press mechanism to stop the bit comes into its own. Before switching the drill on, lower it to the surface supporting the glass. You can adjust the mechanism to stop the press just as it reaches the support surface. Then place the glass under the press and the turn the drill on to begin the drilling.
• Don't push hard as you come to the end. Don't push down any harder on the drill press levers than you comfortably can with the tips of your fingers throughout the process. Keep it steady. Listen for the sound of diamond grinding glass.

All these things will help to avoid chipping out the glass at the bottom of the hole.


Keeping things wet

Using a drill press
Drilling with a Flushing Head
Avoiding chipping
Drilling holes with copper tube and grit
Drilling tools
Drilling glass without a drill press
Hole Placement
Drilling speeds for diamond bits

Drilling Glass, 5

Drilling holes with copper tube and grit

You can drill holes by using loose grit and a copper tube of the correct diameter. It can take quite a while. You will need to have a chuck big enough to take the tube, or have a means to reduce the tube diameter to the chuck size. Alternatively, use core drills that have had the diamonds worn away.

Prepare the glass as for a drill press without a flushing head, so the water and grit are confined. The dam can be putty, plasticine, clay, or other mouldable material put around the area to be drilled.

The grit can be sandblast grit or other abrasive of about 100 to 200 grit.

Drill as normal.

If the core gets stuck in the bit, knock it out with some stiff wire or a nail. Always remove each core right after drilling. They are very difficult to remove if there is more than one in the core of the bit.

For other tips on glass drilling see:
Keeping things wet
Using a drill press
Drilling with a Flushing Head
Avoiding chipping
Drilling holes with copper tube and grit
Drilling tools
Drilling glass without a drill press
Hole Placement
Drilling speeds for diamond bits in glass

Drilling Glass 6

There are a variety of tools that can be used to power glass drills.

Dremmel and similar craft motorsThese are light duty high-speed drills. Those with variable speed controls are especially useful. They work best for small diameter holes. They must have the speed turned down for drilling, especially for larger holes.

These can be combined with a flexible drive shaft for lighter weight.

Drill pressHowever, the most important thing to have when drilling glass is a drill press. Doing it by hand is very difficult and wears out diamond bits very fast. Dremmel and others make drill presses for their tools.

Drilling machinesPurpose made glass-drilling machines are important for larger holes and production work. Flushing head adapters are available from suppliers that will convert a standard drill press into a glass-drilling machine. These tend to be much slower than the Dremmel style motors, but are very steady. The important thing about these is that they use hollow core drill bits, allowing the water to be fed through the drill bit directly to the glass-drilling site.

Drill bits
The other tool needed is drill bits. The recommended type depends on the size of hole to be drilled.

Small diameter holes, up to and including 3mm require solid bits. These can be spade (unusual) or solid diamond-tipped bits. A number of manufacturers make solid drill bits from 2-6mm and some (especially lapidary suppliers) make the very small diameter bits from less than 1mm to 2mm.

Larger diameter holes are best drilled with hollow core bits, as less glass needs to be removed to achieve the hole. These can be used with a flushing head or simply by directing water to the drill bit, with a dam to hold the water around the site.

The bits will last longer if you use a drill press. The press keeps the bit wobble to a minimum and maintains the vertical, both helping to reduce the wear on the bit.

Hollow core bits
Hollow core diamond bits are of two types:

One -where a heating process attaches the diamond - is called sintered in Europe and a number of other countries.

The second – where the diamond is bound to the metal with resins and other chemical attractions – is called bonded in Europe.

Bits of the first type are longer lasting and more expensive. These can be dressed with an aluminium oxide dressing stick to maintain their effectiveness.

Bits of the second type wear quickly and should not be dressed.

In general a diamond core drill breaks out much less glass at the bottom of the hole than a solid drill bit.

Water pumpA further tool that is useful to have is a re-circulating pump. This can be a small fountain pump with a flexible spout to aim the water on the drilling site. A foot switch can control the water flow. A large tub is required to act as the catch basin for the water that comes off the drill and as the reservoir for the pump.


For other tips on glass drilling see:


Keeping things wet
Using a drill press
Drilling with a Flushing Head
Avoiding chipping
Drilling holes with copper tube and grit
Drilling tools
Drilling glass without a drill press
Hole Placement
Drilling Speeds for diamond bits

Drilling Glass, 7

Drilling glass without a drill press

It is best to have a drill press for drilling holes in glass, but there are ways of doing it with a hand drill.

Make a ring of modeling clay, plasticine, putty or other mouldable material about 5cm in diameter and press it around the drill site. Fill the ring with water and a little diamond coolant if you have it. The liquid will cool the drill site and surrounding glass as well lubricate the drill bit.
Adding diamond coolant to your water extends the life of the bits. Buying better (more expensive) bits is worthwhile as they work much better than the cheaper ones.

Use a paint pen to mark the spot where the hole is to be. Without a drill press, starting at an angle with a slow drill speed will stop the bit from sliding around as you establish the drilling point. As the glass surface is roughened, bring the drill to vertical. Move the drill up and down a little as you drill to allow the water into the hole. If you are using a solid or spade drill, a little oscillation keeps the bit from jamming in the hole. Do not do this with a core drill.

A Dremel running at top speed is way too fast. Slow it down with the speed control.
Every diameter drill bit has an optimum drill speed. The smaller the bit is, the faster the speed required.


For other tips on glass drilling see:


Keeping things wet
Using a drill press
Drilling with a Flushing Head
Avoiding chipping
Drilling holes with copper tube and grit
Drilling tools
Drilling glass without a drill press
Hole Placement
Drilling speeds for diamond bits in glass

Drilling glass, 8

Hole Placement

The general rule on drilling holes in glass is that the edge of the hole should be further away from the edge than the thickness of the glass. This means that the edge of the hole on a 6mm thick piece of glass must be more than 6mm from the edge of the glass.

The calculations are simple arithmetic. You calculate the centre point of the hole by adding the radius of the hole to the thickness of the glass plus at least 1mm. For example, to drill a 10mm hole in 6mm glass, you add 5mm (radius of hole) to 6mm (thickness of the glass) plus 1mm = 12mm as the minimum distance from the edge of the glass to the centre of the hole.

Remember this is the minimum distance. For safety and durability in architectural or heavy circumstances, an additional margin must be added.


For other tips on glass drilling see:


Keeping things wet
Using a drill press
Drilling with a Flushing Head
Avoiding chipping
Drilling holes with copper tube and grit
Drilling tools
Drilling glass without a drill press
Hole Placement
Drilling speeds for diamond bits in glass

Drilling Glass, 9

Drilling speeds for diamond bits in glass

Diameter 3-4mm
Speed 6000 rpm

Diameter 5-8mm
Speed 4500 rpm

Diameter 9-12mm
Speed 3000 rpm

Diameter 13-16mm
Speed 2500 rpm

Diameter 17-25mm
Speed 2000 rpm

Diameter 26-28mm
Speed 1800 rpm

Diameter 29-44mm
Speed 1500 rpm

Diameter 45-64mm
Speed 1200 rpm

Diameter 65-89mm
Speed 900 rpm

Diameter 90-120mm
Speed 800 rpm

[Based on CR Lawrence and Amazing Glazing recommendations]


For other tips on glass drilling see:


Keeping things wet
Using a drill press
Drilling with a Flushing Head
Avoiding chipping
Drilling holes with copper tube and grit
Drilling tools
Drilling glass without a drill press
Hole Placement
Drilling speeds for diamond bits in glass

Kiln Shelf Breakage

Placing moulds directly on shelves can cause breakage as my kiln keeps reminding me. If you put a mould directly onto the shelf, it apparently keeps the kiln from evenly heating the shelf on the way up and the mould keeps the shelf hotter than the edges on the way down. I don't know whether the shelf breaks on the way up -although I think that is so - or the way down. It doesn't happen every time, and that's why I forget.

It seems there is a critical relationship between the size of the shelf and the size of the piece covering the mould. The greater the proportion -up to some maximum, maybe 90% - the greater the likelihood of breakage it seems. A fully covered shelf would heat and cool along with the mould. When the mould is small in relation to the shelf, the heat can travel under the mould well enough to avoid breaking, it appears. It is the large range in between that causes the trouble.

A preventative is to fire without a shelf. But failing that possibility, raise the mould a little from the shelf with kiln furniture or pieces of thick fibre paper. Also keep the shelf elevated a little from the floor of the kiln.

Grinding to Shape

There are lots of ways people use to keep marks on the glass while grinding.

Paint markers will stand up to a lot of water if allowed to dry before being taken to the grinder.

Covering the marker line with Vaseline or lip salve will preserve the line longer.

Sticking down a water proof pattern piece on the glass will allow grinding up to the edges of the pattern piece without it breaking down. But of course, it can be ground away or pushed aside by the grinding head.


All these methods assume that there is a lot of grinding needed.

If you cut accurately, only a small amount of grinding will be needed and permanent felt tip/marker on glass lasts long enough to do the job.

Rapid Heat Rises and Their Effects on Firings

Based on a communication from Phil Hoppes

A word of caution. Never use 9999 for a ramp up. Note: 9999 just means on an up ramp the elements are full on, no cycling. On the down ramp the power is completely off until the desired temperature is reached. Your kiln will rise in temperature limited by 2 things - the type of insulation and the number of elements. This can be anywhere from 300 – 450C/hr. to as high as 1600C/hr.)

If the time it takes to go from your lower temp to your upper temp is less than 40 minutes, your controller will be unable to accurately control the top temperature. For example, if you want to ramp from room temperature (20C) to 300C and for your kiln 9999 on an up ramp is 850C/hr., the temperature rise you are looking to accomplish is 280C and your kiln will reach 300C in just under 20 minutes. The problem is that most controllers need around 40 minutes in any ramp cycle to "learn" how the kiln is responding to the inputs that are given to it by the controller. Slower ramps need less “learning” time, faster ramps need more time.

What will happen if you programme a ramp shorter than your controller will respond to is that the temperature in your kiln will not stop nicely at the programmed 300C. The controller has not learned how to stop your kiln from rising in temperature yet and the temperature will rise much higher than your programmed value.

Depending on your kiln and your controller this can be quite significant. Most controllers have a peak shut off value, somewhere between 55C and 85C above your programmed amount. Some controllers allow you to program this value also. If the temperature in your kiln overshoots the value it was programmed to stop and the amount of overshoot exceeds the programmed shutoff temp your controller will shut down. This is a safety feature and the controller is doing what it is suppose to do. If you have something in your kiln however and this happens it will not be annealed properly and you will have to very carefully re-fire to remove the stress or it will break into pieces.

It is a good idea to know just what your kiln will do. You can do this by taking an empty kiln, program 9999 in an up ramp from room temp to 815C. This is the typical peak you would use in a full fuse. See how long it takes for your kiln to reach this temp. This will give you the maximum up ramp rate of your kiln. You can use this rate to calculate if you violate the “learning” margin of the controller. 

It is advisable not to exceed 350C/hr up ramp unless overshooting the top temperature does not matter.

The 9999 ramp in almost all cases will be used to go from the top temperature to the start of the annealing cycle.