Frequently Asked Questions

Kiln and Firing Technical Guidance

1.Q. How do I take a Rohde Kiln apart to move it through doorways?

A. Assuming you can’t wiggle the kiln through the doorway you can take it apart (at your own risk) – many many people have done it – it just needs planning, a number of people with steady hands. Make sure you have enough people to securely turn the body on its side to walk it through the doorway.

The steps are:-

  • Have some blankets to put the various sections onto and remove the shelves and anything inside the kiln.
  • You can remove the lid by removing the black suspension arm (see next step) and undoing the large bolts separating the lid/ top hinge from the bottom body hinge.
  • To remove the suspension arm with the lid closed, remove the clip from the end of the suspension arm nearest the front – you will need a small flat bladed screwdriver – do not lose the clip. You can then remove the arm from the lid hinge (you can take it off completely so that it does not get in the way).
  • Then undo the big bolts and lift off the lid.
  • There are two split pins that connect the body to the bases/legs – carefully lift the body off and place on blanket.
  • Take the the leg/base through the doorway first and place it into position, then bring through the body – carefully line up the clips as close as possible before lowering into place, gently adjust position to be fully lined up – reconnect the clips and split pins before replacing the lid.
  • Line up and put on the lid and re connect the bolts – you can only put the suspension arm on with the lid in its open position!!
  • Check that the black lid safety switch roller pops through the hole on the left side of the lid hinges when the lid is shut.

2.Q. What is “Firing In” – what do I do the first time I fire the kiln ?

A. You will usually see the first programme in a controller is a “firing in” programme, if not you can use a programme that goes to around 1050°C :-
Stack the shelves in the kiln with props in between to dry them and the kiln bricks out (they will have been originally cut by water jet cutters) but put nothing else into the kiln. You can put batt wash on one side of the shelves. If using a firing in programme it will take the kiln up to temperature and hold it for quite some time – it creates an oxidised layer on the elements which will help protect it from sulphates and other gasses/materials that come out of the clay and glazes and so extends the life of the elements.

3.Q. When do I use a bung, exhaust plug ?

A. Many manufacturers do not supply one as they feel using it at the wrong time is more of an issue than not using one at all. The Rohde kilns do come with one – we recommend NOT using one when bisque firing (or not until over 750°C) and only putting it in when the temperature in the glaze firing is above 300°C. There is also an air vent handle at the bottom front of the kiln – only close when the bung is in. You can take the bung out once the kiln has come down in temperature by 100 degrees from the target temperature, but you do not have to – many people fire at night and take the bung out when they get up in the morning or do not use one at all.

4.Q. Can you explain the difference between 13 amp Plug-In kilns, Single Phase and Three Phase kilns? I need something bigger than a 13 amp plug in kiln – do I have to pay for Three Phase to be fitted ?

A. a normal UK house, shop or commercial unit has 13 amp sockets. If they do not have many items taking power from that same circuit, a 13 amp plug-in kiln can work quite successfully being plugged into one of them. Single Phase is when an electrician fits a dedicated cable of sufficient thickness all the way from the consumer unit (fuse board) to where the kiln needs to be plugged in – it does not need special power from the electric company. Three phase power is very rare in a normal house or garage in the UK, it is very expensive to install in the UK but some houses that used to be a farm or workshop do already have it fitted.

  • The kiln will be restricted on it’s size and what temperature it can achieve depending upon the level of insulation in the kiln – the typical 13 amp kiln size is 40-45 litres or 60 litres. High insulation models such as Rohde Ecotop 43 13 amp kiln can easily cope with medium to high stoneware – 1230-1280°C – many of the smaller ones or larger well insulated ones will be good for gentle 1230-1250°C but some 40-60 litre 13 amp kilns we have tested do struggle to get much past 1180-1200°C. Ask us. Some brands state 1320°C on the side of the kiln but that is just a standard print on all of their kilns.
  • We have seen houses that suffer from voltage drop from the local substation (winter / busy times) which can reduce the power in a 13 amp kiln by up to 10% – this can make it difficult for a kiln to achieve high temperatures.
  • Also, it is highly recommended that you make sure that the wires in the socket are nice and tight as if loose the socket can overheat and smoke – hopefully tripping the breaker in the fuse board / consumer unit. We do see this a couple of times a year after new kiln deliveries. We have sold over 700 plug in kilns over the years and not had any cause problems more than a blackened socket – which were in all cases we believe due to loose wires in the socket.
  • Single Phase is when an electrician fits a dedicated cable of sufficient thickness all the way from the consumer unit (fuse board) to where the kiln needs to be plugged in. Many people buy 60-100 litre kilns 23-32 amp kilns to go into a specially fitted 32 amp socket so that they can do high stoneware and porcelain; some electricians are happy with running cable for kilns up to 40 amps for kilns up to 130 litres, even 48 amps for kilns up to 150 litres.
  • Kilns using between 32 amps and 60 amps are common in small industrial units but you do have to check if you are sharing the total incoming ampage with other units. We do have some houses and commercial premises, such as shops, using kilns with up to 60 amps on a single phase but do check with your electrician.
  • Single Phase and Three Phase kilns can use thicker elements that 13 amp plug-in kilns meaning that they can last significantly longer.
  • three phase electric supply is more efficient and less problematic for motors and machinery like kilns that come on and off power during the firing – it is very expensive to install in the UK but some houses that used to be a farm or workshop do already have it fitted.

Just because you need a kiln bigger or more powerful than 13 amps does not mean you have to use Three Phase – you can have an electrician fitted cable from your consumer unit/ fuse board and this is known as Single Phase.

5.Q. Can I use an extension cable with a 13 amp plug-in kiln?

A. 13 amp plug-in kilns require the whole 13 amps – even with high insulation models they do need all 13 amps. Please do not use an extension cable – plug straight into the socket – they can steal 15-20% of the voltage at low temperatures and 20-25% of the voltage at high temperatures. If you have to use an extension cable there are some specialist heavy duty, low power loss ones available on the internet using 24 amp rated cables but with a 13 amp plug on one end and a 13 amp socket on the other.

6.Q. Do I need to use Orton Cones – what is gentle firing?

  • The modern kilns are controlled by thermocouple and digital controller but the bigger kilns without floor heating, and without the most modern insulation, may have colder spots – the first time you fire the kiln full it is worth putting some cones throughout the kiln to get a picture of the difference in heatwork throughout the kiln.
  • You may notice I said heatwork, not temperature, as cones do NOT tell you the actual temperature – they bend based on heatwork – time and temperature. For example a “6” cone will bend at approx. 1222°C if the last hour of the firing was at 60°C per hour, but bend at 1243°C if the last hour of the firing was at 150°C per hour. The heatwork is created by time and temperature – fast and high temperature or slow and lower temperature can fire the glazes and clay in the same way. In the same way as it is heatwork that affects the cone not just the final temperature.
  • Some people when they move from a cone operated kiln to a digital controller kiln have to lower their firing temperature to match their original heatwork as really they had not been going as high in temperature as they thought. Gentle firing to a slightly lower temperature replicates what their old kiln was doing / replicates what kilns did when glazes and clays were developed.
  • Many glaze manufacturers like Mayco put the cone numbers on their glazes not a temperature – on their website the technical information states that the cone numbers are based on the last hour being at 60°C per hour.

7.Q. My kiln is over-firing but my friend says that my elements are wearing out – how can that be?

A. As the elements start to wear they take longer to get to the target temperature – maybe an extra 20 minutes – this is like going to a higher cone number or going an extra 18-20°C – so the glaze can have absorbed more heatwork / be over fired, such as colour burned out or blisters. To make elements last longer before you have to change them (or give you time to order some) you can lower the target temperature a little bit each time – once you have seen this phenomena.

8.Q. Can I test an element with paper / how do I know if the element is wearing out?

  • A. You can put a small piece of paper (not glossy as it will stick to the element) on each element and fire the kiln for 10 minutes to see if the paper burns/scorches – and then with the kiln disconnected from power carefully remove the paper with long-nosed pliers / vacuuming any bits. This proves if electricity is going through the element or not, but not how worn out the element is.
  • An element will wear very slowly until towards the end of its life when the wear speeds up. If the rings are collapsing over it is on its way out – you may see some over-firing as the kiln is taking longer and creating more heatwork. You can lower the target temperature a few times to accommodate this whilst you order new elements.
  • If elements have moved forward or hanging down, it is best to heat it up before trying to bend it back as they can be fragile at that stage in their life – heat up and then use long-nosed pliers to move them.
  • How easy is it to change elements on a top loader ? Most people do it themselves. There are plenty of You Tube videos. Often people do get a kiln engineer, or local electrician, to fit them the first time and carefully watch how they were installed. We have the most popular Rohde and Nabertherm elements in stock, as well as a few Kittec elements. We do recommend ordering them as soon as you think the elements are starting to go. If a commercial pottery, we do recommend you have a spare set in at all times just in case, and then ordering the next ones when you change those ones.

9.Q. Can weather affect my kiln?

A. A very cold workshop will mean that the kiln is having to work harder and may not go up as fast as you have set the controller to achieve – it is possible it will error out – set it going again but with a slower start rate.
Also, if colder inside the kiln than the rest of the room the thermocouple inside the kiln needs to be warmed up so that it reads correctly – I have a customer in Sweden that uses a hairdryer inside the kiln for a few minutes before starting .

10.Q. Do I need a soak at the end of the firing?

A. Tall and wide kilns without floor heating can have relatively big differences in temperature between different areas of a kiln. You may wish to have a soak to give it extra time to even out the temperature. Though with heat rising the top will still be hotter than the bottom. Not firing too high and then having a soak enables a slightly higher level of heatwork without your kiln going as high – a fifteen minute soak is about 5 degrees more heatwork. People who fire fast often have a longer soak than people who fire more gently to a similar target temperature. See Question 6 for more discussion on heatwork.

11.Q. Batt/kiln shelves – firing in, batt wash, floor shelf?

  • A. We recommend putting a shelf on the floor (on top of the little blocks that kiln manufacturers usually provide) to protect the bricks from glaze runs which could enter the pores of the bricks and then expand and contract potentially splitting the bricks.
  • When first getting a new shelf gently fire it to 200°C+ to get out the moisture. Most shelves are cut by water jet and contain a lot of moisture from the manufacturing process. Otherwise when first used the shelf can crack or become stressed at the point where an item is placed on it due to the moisture / steam being preventd from getting out.
  • We do recommend using batt wash powder which has been turned into a paste with water on the upper surface of the batts – over time it will flake off so should be brushed to get rid of loose material and touched up.
  • When you are using a number of shelves in the kiln put all of the props vertically in line with each other. This is so that the weight of all shelves is transmitted through the props to the floor – or you will end up with bent shelves.
  • For wide shelves going to stoneware do use thicker shelves to prevent sagging.

12.Q. When should I open the kiln lid?

  • It is best to let it cool down to ambient / room temperature before fully opening the lid.
  • If wanting to encourage crackle glazes to crack you can open just above 200°C.
  • You can open vents, bungs and crack open the lid a little to help the high insulated kilns cool down a little quicker from 100°C.
  • Opening early can cause cracks in clay and glazes that you do not see for weeks; and also, can cause fine stress cracks to the brick work.

13.Q. It is my first firing and the kiln smells, is this OK? Exhaust ventilation?

  • A. The first time you fire there will be organic matter in the bricks that will burn out. With some clays and glaze binders you will also get smells but the smell will die away above 600°C. Paper clays particularly will smell.
  • Good ventilation is important but depending where it is placed can be just an open door or window, or just the gaps where garage walls and roof meet.
  • We do supply flexible stainless steel exhaust hose which can be fastened to exhaust brackets on kilns – the exhaust bracket sits above the exhaust hole but does not cover it completely. This gap has been created purposefully following testing by the main German kiln companies. Typically you would use a maximum of a 3 metre length – going vertical for about a metre, then a gentle curve to horizontal. This can then be pointed at an open window or connected to a hole in the wall covered by a vent grille to discourage insects and birds etc wanting to come into the warm kiln. Heat rising is usually sufficient to carry the moisture etc and so mechanical extraction is not usually required.

14.Q. Some of the bricks have fine cracks in them / or indentations – is this a problem?

  • A. The bricks are made with small bubbles in them to aid insulation (like a duvet) – when cut these can be on the surface and do not affect the insulation properties of the brick. The heating and cooling of the bricks in the kiln can lead to some fine non-structural cracks which are rarely anything to worry about.
  • If opening the kiln early to encourage glazes to crack you can also be encouraging bricks to crack.
  • The main source of cracks in bricks is physical shock to lids- such as not being closed carefully. Often the result of this shock is not seen for months until the kiln has been heated and cooled several times. In addition we have seen where powders such as glazes, powdered clays, oxides etc getting into the pores of lid bricks from bags temporarily placed on top of the kiln or settled on to it and then expanding and contracting.
  • We recommend placing something over a kiln lid at all times to protect it.

15.Q. How close to a wall can I put my kiln?

  • A. Kilns are getting more insulated and so are more like a hot radiator these days but … you would not want to place it near any nice kitchen cupboards for example – it will discolour wood through heating up the area. Preferably 18” clearance all round and if it cannot be more than 12” you may want to put some reflective material on that wall.
  • Do not place anything flammable near it just in case especially in front of the exhaust hole. The exhaust hole is where the majority of the heat comes out and so it is best if that is pointed into an open area.
  • Do NOT leave anything sitting on top – you do not want the controller to melt into the surface of the lid nor the heat burn out the electronics.
  • As heat rises the air underneath a kiln does not get that hot but it would discolour a wooden floor – many people put kitchen ceramic floor tiles underneath or boards known as Concrete board / tile backer board/ cement board.

16.Q. What gasses come out during firing / when do the chemical reactions happen?

  • A. During bisque firing from 100°C to 200°C free moisture will turn to steam, and up to 500°C the remaining water in the clay capillary tubes will continue to come out as steam.
  • This has to make its way out and will get out by the easiest routes – if you have put underglazes on to greenware this is when it may peel off or the steam create cracks in the clay if the firing rate is too fast or if you have made an enclosed globe this is when it may explode if there are no holes for the steam to escape.
  • One teaspoon of water makes about 1.5 litres (coke bottle) of steam.
  • Especially susceptible to cracking are smooth-bodied and low porosity clays like white earthenware if fired too fast.
  • Above 500°C the remaining moisture will chemically bond with the clay which is then classed as dehydrated and be strong enough to be classed as ceramic.
  • Up to 600°C we recommend going no faster than 100°C to for the first 150-300°C and then 130-150°C per hour.
  • From 600°C towards the target temperature you can go at 150°C per hour (some people go as fast as 250°C). However, we recommend for the last hour of firing up to the target temperature that you then slow down to 60-80°C – enabling a lower target temperature and more even firing throughout the kiln.
  • From 650-750°C carbonaceous matter and sulphate should have finished burning out.

17.Q. Placing work inside the kiln?

  • A. Un-glazed pieces can touch each other / glazed pieces can’t.
  • Use a shelf on the floor (on props or thin pieces of refractory supplied by the kiln manufacturer) – do not place pieces directly on the floor bricks.
  • Leave a gap above work before placing a shelf or there can be hot spots making the glazes bubble and blister.
  • Leave a 1” gap between work and the elements – be careful with mug handles.
  • A half empty kiln will use a lot more energy to heat up – if you really need to fire it half empty you can always put in a couple of insulation bricks.
  • Batt wash the shelves to prevent sticking of runny glazes – maybe use wax resist on lower quarter of the pot to prevent runs.
  • Open the kiln lid as close to room temperature as you can to prevent cracking of clay, glaze or brickwork.

General Information and Delivery

1.Q. Do you deliver the kilns and install them yourselves?

  • A. No – we do not use our own staff and vehicle – we have deliveries of clay, goods and kilns being delivered all over the country most days and so use a pallet network. Pallet delivery is to the roadside by a pallet network tail lift vehicle – we will book in with you with plenty of notice so it will be a specific day and you can choose an AM service.
  • However, you will need help with you on the day – the driver will lower the pallet down and then can only help with their pallet truck if it is a completely flat, hard surface – no slopes, kerbs, gravel, cobbles etc.
  • Please have a plan for the day it arrives – check the doorways etc to make sure that the kiln fits through and fits where you intend to position it. Please a) check it thoroughly before signing for the kiln and b) take the shelves and any boxes, glazes etc out of the kiln before tilting / moving the kiln.

2.Q. Is delivery part of the price?

A. Delivery charge is separate as it would not be fair on people living close to us to be charged the same as someone living far distant or where a ferry is required. The link to the pallet delivery charges is on the bottom of every page.

3.Q. Does the kiln have wheels/castors?

  • A. Rohde Ecotop kilns up to 60 litres and Rohde TE75MCC and TE110MCC have two wheels at the back that come into play when the kiln is tilted. All other Rohde kilns have an option to buy 4 castors/wheels (two with brakes)
  • Kilncare top loading kilns come with castors/wheels as standard.
  • Nabertherm top loading kilns have light duty transport castors as standard with the option of heavy duty ones.

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