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Leadlighting Tutorial Lesson 5: Measuring and other things you need to know.

This lesson is really the very first lesson for leadlighting simply because all the measuring for windows and door panels must be done before drawing a cartoon and cutting the glass. But for most people, unless you are fascinated by simple maths, this probably isn't the most interesting lesson. It is however, a necessary part of leadlighting and I have slotted it here to maintain your interest and also it will be more easily understood.

The standard measuring instrument is a steel tape marked in millimetres. Don’t use a dressmaker’s tape, as they tend to stretch.

Measuring is a simple operation, but so critical. The absolute rule is check, then CHECK AGAIN. Force yourself to do it, it's better to be safe than sorry! It only takes a minute to re-check it, who knows what to fix it.... (Measure twice, cut once.)

There are two areas where mistakes are made:

1. Measurements taken from the frame.

This really needs no explanation but it usually happens when you are rushing or careless. (If you wear glasses make sure you wear them, 3,5,6,8 & 9 all look similar without glasses. Trust me, I'm human too and I've made this mistake.) Most times when you measure for the second time you usually pick it up, but if you miss it again, well what can I say.

2. Transferring these measurements to the cartoon.

You may be forgiven for thinking how could a mistake be made in transferring the measurements to the cartoon? This is a classic mistake, I've done it and it's such an easy mistake to do. Let's say you're making a full length sidelight and the height was 2040 mm or 2 mtrs 40 mm. Next you go to your cartoon and use your tape measure to mark off the height on the cartoon. But because the clip on the end of the tape isn't easy to use as a starting point for the measurement, you measure from the 100 mm mark on the tape simply because it's a more accurate starting point. You even get someone to hold the tape where you've marked the cartoon at 100 mm so that it doesn't move. Then you concentrate on marking the cartoon at the 2040 mark on the tape because you know the height is 2040 mm. So far so good right, ......or is it? You've probably already guessed what happened, I had forgotten to ADD ON that 100 mm that I deleted in the first instance by measuring from the 100 mm mark on the tape. My embarrassment in this instance may benefit you! I was very lucky, because the design already had a border around it and I was able to put an extra 50 mm border top and bottom. If the design never had a border it would have meant major surgery. I never made that mistake again.

I will address wooden windows, including door panels, shaped panels, circular windows and lastly, aluminium windows. Wooden windows first.

Firstly establish the rebate size in all instances to know what outside lead to use: (Halve the difference between SIGHT SIZE and TIGHT SIZE - see diagrams.)

E.G. if the tight size was 645 mm and the sight size was 625 mm, the difference is 20 mm. So half the difference is 10 mm, which makes the rebate 10 mm, and we would use a 12.4 mm H lead around the leadlight because we want to see in all instances, a 3 mm lead margin in the sight size area. In this instance we use the 10 mm formula below. This will become clearer working through the measurements in the diagrams.

The GLAZING SIZE (or fitting size) can only be established once we know the rebate size, which is derived from the tight and sight sizes.

The diagrams below refer to three sizes we need to consider when measuring.



Formula for windows with a 10mm. rebate: Sight size + 18mm = Glazing size.


EG. Sight size = 850 x 450

Add 18 to both above measurements for the glazing size.

(To explain where the 18 comes from simply. Because we are using a 12.4 H lead in this example and we want to see a 3 mm lead margin all round in the sight size area and 9 mm of this lead is extending into the rebates on either side, so 9+9=18 - refer to above diagram and formula.)

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Glazing size = 868 x 468 < This size draw in pencil then come in 6.5 mm all round for the cut line. In this instance you will use a 12.4 H lead as per diagram above.

The 1 mm either side of the lead in the rebate is the clearance - 2 mm in total.

Formula for windows with an 8mm. rebate: Sight size + 14mm = Glazing size.


EG. Sight size = 825 x 475

Add 14 to both above measurements

Glazing size = 839 x 489 < This size draw in pencil then come in 5.5 mm all round for the cut line. In this instance you will use a 10 mm H lead.

As most frames have a rebate of either 10 or 8 mm deep, by using the correct outside H lead for the rebate, there will be a 3 mm lead margin in both instances.

Some older frames may have an even smaller rebate, just 6 mm. A 10 mm H lead is still used but the formula changes to Sight Size + 10 mm = Glazing Size. This will still enable a 1 mm. clearance all round, or 2 mm overall as in all above instances, but more lead is exposed on the sight size. Can you work out what it is?

Note: Some of the older doors can have deep rebates, up to 100 mm. If you make the leadlight to fit in the rebates to the TIGHT size, part of the design will be lost behind the beads if you forget to design accordingly.

There are two ways to address this. One is to use the 10 mm. formula so that the leadlight will extend into the rebates by 9 mm all round. To centre the leadlight vertically in the frame, two blocks of timber 91 mm. high x 7 mm thick are used as supports. (This measurement is for a 100 mm rebate, but would need changing if the rebate was less than 100 mm - it's just a simple matter of deducting 9 mm from whatever the rebate size is for the supports.) Depending on the type of beading used, a small panel pin is used on both sides of the leadlight to centre it.

An easier way is to make the leadlight to fit to the rebate but make allowance in the design, i.e. the design ‘begins’ in the sight size area.

Having read all the above, most will have realised you can measure the Tight Size and subtract 2 mm to give the Glazing Size. That's the lazy man's way and can lead to mistakes! Suppose you didn't measure the Sight Size and it was actually 50 mm smaller than the Tight Size, which means it is a deeper rebate than normal and I've already said what will happen there. If you only measure the Tight Size, how will you know what outside lead to use? When you think about it, it's just as easy to add either 14 or 18 to the Sight Size than subtracting 2 mm from the Tight Size.


Measure left, right and centre on height and repeat for width. Reason for checking centre, is that some large timber frames can have a bow in them either way, in or out. You will need a good metal ruler to use as a straight edge with you, as measuring alone will not tell if it is top or bottom or the sides. Check diagonally to see if the frame is square. If the numbers aren’t the same, it means the corners aren’t right angles, Take a square to check as well. If there are large anomalies, the leadlight can to be made to suit. This usually only happens on very large frames.




For both the older and modern styles and kitchen cupboards.


Some kitchen cupboards can have an arch at the top as well as a door panel, which can have an arch on both ends, top and bottom. In the case of a kitchen cupboard, the rebate will either be recessed out with a router on the reverse side to the same shape as the opening, or it will be routed out square, simply because it's easier to measure and cut the original glass to a straight rectangular shape rather than a curve. If the rebate is a curved shape at the top, place a square of clear glass over the opening on the rebate side, making sure the glass is slightly larger than the opening so that you can first cut the curved shape exactly to fit the rebate while it rests over the rebates on the door. After removing the waste piece, place the glass back over the rebate leaving about 3 mm clearance at the top and with another pair of hands to stop the glass from moving - then score the remaining 3 sides at the same time while it is still over the rebate, leaving about 3 mm clearance on each side, but definitely no more, providing the rebate is NO wider than 10 mm. (See below under NOTE.) This is so that when you trace around the glass template with a pencil onto your cartoon material, which represents the outside line, you will actually be drawing it a little larger than the glass template. Just make sure of one thing, check to see if the glass template will fit the rebate on both sides of the template by reversing it as sometimes the arch may not be a mirror image and the template only fits one way. If this IS the case, with the glass fitting in the rebate, mark 'face' on the front side of the glass and then put it on the cartoon with 'face' UP. This is very important because any textured glass in the panel will then be on the inside of the cupboard, making it easier to clean, you don't want textured glass to be on the outside in a kitchen cupboard. When assembling, start from the bottom, which will be a square edge and the last lead to go on will be the curved edge and you can pre-bend the lead to the template shape to make it easy to fit. In this instance you use horseshoe nails to hold this lead in place while you solder it.

If the rebate is square across the top, (on the back, as mentioned in the beginning of the above paragraph) but there is still a curved shape when viewed from the front, which means the leadlight will be a rectangular shape. Still cut the glass template (a rectangular shape) the same way allowing the same clearance all round then trace around the glass template onto your cartoon first. You will be making the panel to this rectangular shape. You are not finished with the template yet. Then place the glass template in the rebate and 'centre' it. (You may need those other hands.) Now from the front of the door, after writing face on the glass, trace the curved opening from the front of the door onto the glass with your cartoon pen and cut on the line separating the glass. Now that you have 2 pieces of glass with a curve cut in them, it doesn't matter which piece you use to trace the curve onto your cartoon in the right place. Now that you have a curve drawn on the cartoon, draw the cut line around the perimeter of the rectangular shape, then you can draw the rest of the design. (Keep the small end of the template with the curve to use as a fill on top of the curve in the cartoon, after trimming it to size on the cartoon, don't worry if it breaks in the middle of the curve.) Again start assembly from the bottom edge and when you get to the curve, you use a 6 mm square H lead on this line. This is so you will still have a 3 mm lead marginal all round rather than glass disappearing behind the wood at the top. You may find that it is quite narrow on the top of the curve, in which case you will either have to cut a curved recess in the outside lead to fit around the 6 mm lead or cut a flat on top of the curved 6 mm lead so that the outside lead will fit. I find it easier to cut the recess into the outside lead. In most cases, unless it is an older door which may have beading which will simplify the installation, there may only be the rebate and it could be rebated up to 10 mm deep. By using glazing foam in the rebates and secure it with plastic 'fly screen' clips.

Some cupboard doors may not have a rebate at all because the original glass was cut 10 mm or so larger all round than the opening and secured with plastic fly screen clips. In this instance you can use a Y13 lead around the leadlight and still secure it with the fly screen clips. Before removing the glass from the fly screen clips, trace around the opening from the front - remove the glass and cut the shape, then trace around the template onto your cartoon material in pencil. Then it's a simple matter of measuring out 6 mm from that pencil line, which came from the tracing of the template and now becomes the proper outside line of the leadlight, then come in 9 mm from the outside line for the cut line. (It's probably a good idea to rub out the 'first' pencil line after you've established the true outside line to avoid any confusion.) A Y13 lead has a nice appearance in kitchen cupboards.

NOTE: If the rebate is over 10 mm wide in both instances, you will need to cut the template to the finished size of the leadlight, which will use a 12.4 lead around the perimeter so that a 3 mm margin is seen all round from the front. You just have to cut the template so that it extends into the rebate by 8 mm all round on each side. By doing this and tracing around the template making the drawing slightly larger, it is effectively ensuring that the finished leadlight extends into the rebate by 9 mm all round, which will show the required 3 mm lead margin all round from the front. The panel may need some support at the bottom to centre the panel.


A simpler way of making a template for a shaped door panel (you can still make a glass template if you prefer) is to remove the beads from the rebates and tape your cartoon material very securely to the rebate side of the door. Some doors have the rebates on the outside, some on the inside. Then with a small piece of lead, take a rubbing of the opening. This can still be done effectively the same way with a panel that is putty glazed. (The putty should be at a 45 degree angle which will allow the rubbing to show the rebate shape, and/or size on the cartoon material.) If the opening is circular, oval or a repeat shape top and bottom, write TOP at the top and FACE SIDE on the cartoon. No matter what side the rebate, write this on the cartoon material as if it was on the outside of the door, not the inside.

If the glass is still in the door and if the rebates are on the inside, you will have to write this information immediately after taking the cartoon material off the door. This is so you will know what side to draw the cartoon on as openings are not always symmetrical and a leadlight is installed one way only. Face refers to the smooth side of glass and the smooth side is always on the outside as it sheds dust easier, with the glass texture on the inside.

(Refer also to where marked * in lesson 2 to avoid confusion repeating it here.)

It is not possible with a shaped opening to use the standard timber formula. To achieve the glazing size, simply come in 2 mm. from the rubbing line for the pencil line. This takes care of any anomalies. The cut line is drawn next, depending on what size outside lead is being used, either 5.5 or 6.5 mm in from the pencil line.

Never glaze a leadlight “dry” into a frame unless there is no chance of rain wetting it, such as under an awning on a veranda. Apart from rattling, rain can easily get between the leadlight and the beads, causing dry rot. Do NOT use silicon as a sealant, if a leadlight has to be removed for any reason, the difficulty in its’ removal can cause the glass to break. The easiest and best sealant to remove is glazing foam. Putty can be used as a second choice. Glazing foam is a double-sided adhesive rubberised tape 7 mm wide x 1 mm thick. It is placed in the rebate if the beads are inside, otherwise on the beads or on the outside lead of the leadlight itself if they are outside. In either instance, you put the glazing foam tape on, then peel off the backing paper and that stops water entry.

Leadlights in timber frames are mostly glazed in with timber beads which are very simple. Just make sure you remove the longer ones first as they will spring out easier and when replacing, reverse it by putting the shorter ones in first. Be careful when nailing the beads back in that you don't hit the leadlight with your hammer, use a punch for that last 5 - 10 mm.

The older method is to putty glaze them in. Sometimes this can be a difficult job if the putty is rock hard, or easy if the putty is loose, either way you must remove the putty down to bare wood. Use an old blunt chisel and hammer. If using the latter method, prior to installation, fold down the outside leaf of the outside lead with a fid as per diagram below. This will enable a larger bed for the putty to adhere to the timber frame as wood sash putty adheres better to wood than lead. A small amount of putty is placed on the vertical part of the frame between the outside lead to form a bed as well.

Note: Use wood sash putty.



If the leadlight is circular, never assume it is a perfect circle, especially timber ones. As with an oval, take a rubbing for a template to be certain. If it is small in size, 600mm diameter or less, it will not require reinforcing.

Use the same technique to determine the glazing size of a wooden circular or oval window as is described above under the formula for timber windows and use the measurements applicable to determine what size outside leads to use after taking a rubbing of the opening from the beaded side. IE. the rubbing line will be the sight size, so establish the size of the rebate from that to give you the tight size - then you will know what outside leads to use. You may simply be able to measure the tight size from the outside of the beads and work from there.

If the opening is putty glazed you can take a rubbing in 2 ways, either from the opposite side of the door to the puttied side, usually the inside of the house, which will be the sight size, or from the puttied side, which will be the tight size where the rebate is and using the method described above in the paragraph under the heading: shaped door panel. If you are taking a rubbing from the inside on a putty glazed door, make sure you mark the cartoon with face and top immediately you take the cartoon material off the door, which will be on the opposite side to the rubbing. One last thing to remember is if you have taken a rubbing of the sight size, (the inside) the glazing size will be outside the rubbing line and you will need to establish the rebate size to know what the glazing size is and which outside lead to use. If taking a rubbing from a putty glazed door from the outside, which will be the tight size, the glazing size will be inside the rubbing line.

The modern oval door usually has a large composite, fibreglass embellishment, which serves as the beading on the outside of the door and is usually stapled or tacked on covering the rebate. This will have to be removed to determine the size of the rebate and a rubbing can then be taken.

If the above seems confusing, reading it through a few times with reference to your door at the same time will help you understand it.


After cutting the glass, it doesn’t matter where you start, being circular there are no timber beads to build into. So, selecting the largest piece on the outside cut line, fix it in place with 3 horseshoe nails and U leads. Build from this piece in the normal fashion until the leadlight is completed, having the leadlight held in place around the entire perimeter by horseshoe nails and U leads. Remember to cut the leads that go out to the perimeter of the leadlight to the correct length so that whatever outside lead being used will fit on completion.



No matter what size the circle put the outside lead on in at least two halves. Firstly, remove only half of the horseshoe nails and U leads. Fix half of the outside lead on and replace the nails and U leads to the outside of this lead. Repeat process for the other half and ensure you can just see the pencil line before soldering, particularly for an aluminium window.

If it is larger than 600mm diameter it will need reinforcing. A timber bead is attached along the reinforcement line and if using 7 mm zinc, the bead is attached 3.5 mm away from the line. The zinc is first placed against the bead then the leadlight is built from the zinc to the outside of the half circle. When the outside lead is held in place with horseshoe nails and U leads, the timber bead is removed and the other half is completed in the same fashion. Remember if it is a wooden window the zinc is cut longer to extend through the outside leads, if aluminium it is cut short to fit inside the Y13. (See lesson 8 about this and also for reinforcing with other methods if not wanting to use zinc.)


When glazing a leadlight in an aluminium frame, it must be remembered that lead and aluminium must not come in contact with each other. When moisture is present such as rain, if they are touching, an electrolytic action is set up between the two metals and corrosion will result. It is called electrolysis.

As there is only one outside lead for aluminium windows there is only one formula.

Sight size + 14 mm = Glazing size.

EG. Sight size = 657 x 425

Add 14 to both above measurements.

Glazing size = 671 x 439 < This size draw in pencil then come in 9 mm all round for the cut line (ink) Note that this differs from H leads.

(For circular windows, add 14 mm to the diameter, or sight size - i.e. 7 mm either side.)

In case it is not a perfect circle you can still take a rubbing, remember to mark the top. From the rubbing line go out 7 mm for the pencil line, then come back in 9 mm for the cut line, which will put the cut line 2 mm inside the rubbing line. (On the drawing below, the sight size will be the rubbing line on the cartoon. This may help clear up how the glazing size is achieved on a circular window by working through the measurements.)


Note: The clearance for aluminium windows is not where you might expect, i.e. the gap between the outside edge of the leadlight and the inside of the frame, as this gap could be considerable on some windows.

The clearance is the 1 mm. gap between the frame edge and the underside of the cup of the Y13 lead. Don’t be too concerned over this as it is no different to the 1 mm. clearance for wooden windows. The only difference is that unlike a leadlight for a timber frame, leadlights for aluminium frames cannot be reduced in size by planning; so all measurements must be double-checked. A last precaution is to check the size BEFORE the panel is soldered.

As most people new to glass cutting, tend to cut slack (further away from the line than normal) rather than full, the leadlight will most probably ‘shrink’ during assembly and up to 5 mm. shrinkage overall is still OK as this is only 2.5 mm either side. This means there is still 4.5 mm of lead of the Y13 covered by the frame. This is acceptable, BUT NO MORE.

If it is smaller, the trick of packing the lead can be used to remedy the situation. BUT, if the leadlight is even 1 mm. too big before soldering, it will NOT fit; the glass will have to be altered.

Aluminium windows are glazed by two methods.

1. An aluminium or plastic bead, the older type and not used much any more.

2. A rubber bead, which is the modern and simpler of the two.

If an aluminium bead is used, after removal of the beads and glass, it will more than likely have a rubber seal which can go around the leadlight. As it is one continuous seal, take care to put the join at the top to stop rain entering. Then snap the beads back in place.

The removal and replacement of these beads is the most difficult part in the installation. There are a number of different types, some easier than others.

If there is no rubber seal and the glass is glazed with an industrial double-sided sticky tape, remove it by softening it with turps and replace with glazing foam. Black electricians tape is placed on the inside edge of the Y13, thus separating the leadlight from the aluminium bead.

If a rubber bead is used, after removal of the beads and glass, once again, remove the sticky tape and replace with glazing foam. In both instances, the leadlight must be centered in the frame BEFORE removing the backing paper from the glazing foam. A helper is needed for this operation. In each corner, peel back 50 mm or so of the backing paper. (8 ends in total) This will enable holding the leadlight against the glazing foam, but still able to move it up, down and sideways to centre it. Small rubber blocks can be positioned under the edge of the leadlight when satisfied it is centered. Holding the leadlight gently against the glazing foam, your helper, on the other side can start to slowly pull the backing paper ends away starting at the top, then the sides finishing at the bottom. The leadlight will now be stuck to the glazing foam. The rubber beads can now be installed pushing them in with your thumb. Soak them in hot water and detergent for a few minutes and they will fit easily.


Leadlighting Tutorial Lesson 1: Cutting Glass for Stained Glass Leadlights the Right Way

Leadlighting Tutorial Lesson 2: How to make a leadlight. Get started with a simple clear glass leadlight. Design choice.

Leadlighting Tutorial Lesson 3: Assembly of a Leadlight and helpful hints.

Leadlighting Tutorial Lesson 4: Soldering a leadlight and using the right flux. Making a tinning pot.

Leadlighting Tutorial Lesson 5: Measuring and other things you need to know.

Leadlighting Tutorial Lesson 6: Advanced Glass Cutting - methods for difficult shapes.

Leadlighting Tutorial Lesson 7: Puttying and how to repair a broken leadlight

Leadlighting Tutorial Lesson 8: Reinforcing - how, when, where and why.


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