There are several kinds of solder available for stained glass work. Are you always using the right kind?
There’s a lot of good advice and information on the Internet. There’s also a lot that isn’t. That’s the trouble with the Internet. So, for this posting, I decided it was time to do some reach useful conclusions about why there are different grades of tin-lead solder, how they perform and reach conclusions about how they are best used.
So, let me guide you by explaining and contrasting what I have learned and experienced with the tin-lead solders we routinely use. But I will not talk about lead-free solders because I never use them.
It’s time to learn and make use of some materials science…
Solder Properties and Behaviours
There are several grades of tin-lead solder available to us, with tin concentrations between 5% and 70% by weight in their alloy mixture. In reality we only tend to use a few of the various grades – the ones that are useful for our craft.
Incidentally, I’ve seen solder described as a compound. This is wrong because an alloy is a mixture, not a compound. Mixtures are when two or more things are brought together but are not chemically bonded together. Compounds are when two substances chemically react to form a third substance. But, as usual I digress.
The important thing to understand is that different grades of solder will behave differently because they are different mixtures and this in turn means they will have different physical characteristics (such as melting point or electrical conductivity). We need to understand how some of the differences might affect our craft work and in turn guide us towards rationally choosing the grade of solder we use for a particular task.
One property of the tin-lead alloys is that the greater the tin proportion, the greater the solder’s tensile and shear strengths. What this means in practical terms is that higher tin proportions result in a “harder and stronger” solder. But tensile strength and shear strengths are not the most important issue for the stained glass worker, though they do have a subtle effect on the structural strength of what is constructed.
Of greater importance to the stained glass worker is how solders perform during the act of soldering. This where our focus is most usefully directed.
From experience you will have noticed that when you remove your soldering iron from melted solder it takes a few moments before it starts to change into a pasty state and then a few more moments until it properly solidifies. Also, if you have experience of different grades of solder you may have noticed that some stay in the liquid and pasty states for different amounts of time than for other grades of solder. You may also have noticed that if you move your work as soon as the solder appears to have changed from a liquid to a solid then you can be surprised to see the solder distorts and seems to turn into a lumpy grey mess (they call this a “bad joint” in electronic soldering). This all hints at there being a two-stage cooling process.
This two-stage cooling behaviour is characteristic of alloys – except for when they are in a eutectic mixture which is a special case.
Unlike pure metals, which have a single clear melting point, alloys have a range of temperatures over which they are changing from a solid to a liquid, or back again. The temperature at which an alloy changes between an entirely liquid state and a pasty state is known as the liquidus temperature. The temperature at which an alloy changes between an entirely solid state and a pasty state is known as the solidus temperature. Exactly what’s happening as the alloy cools down (or heats up) is rather complicated to explain but later I’ll give you a couple of references on the Internet you can study to find out more.
So, when we remove our soldering iron from some solder, it is in the liquid state. It soon cools down and reaches the liquidus temperature at which point it turns into a pasty state and then finally changes into a solid state when it has cooled down at the solidus temperature.
To get even closer to understanding what’s happening when we take our soldering iron away from some solder, let’s assume you have a temperature-controlled soldering iron, such as the Weller 100W, which normally operates at around 370 ºC (unless you use a different kind of tip). Let’s also assume we have a variety of grades of solder to work with – the four we are most likely to encounter.
The reason we want to know the soldering iron’s temperature is because it’s the temperature that the solders will become when heated. Obvious really!
We’re now ready to do some serious thinking. Study at the table below:
If you don’t do tables and are stuck, here are some hints:
- It has rows, one for each of the different grades of solder that we might encounter.
- It has solidus and liquidus temperatures from which we calculate two temperature ranges.
- It lists the pasty temperature ranges for different solders, where the solder is neither liquid nor solid. This is sometimes called the working range (a rather confusing term I think).
- It lists liquid temperate ranges for different solders, based on an assumption that our soldering iron operates at around 370ºC.
And here are the important observations we can make from that table’s information:
- All the alloys change from the pasty state to a solid at the same solidus temperature when cooled. This temperature is the same regardless of the proportion of tin and lead. This means that all tin-lead solders become solid at the same temperature when cooling.
- The alloys change from a liquid state to a pasty state at different liquidus temperatures when cooled so there is link between the proportion of tin and lead and the liquidus temperature.
- We now look at the liquid range temperatures. More tin in the alloy means a lower liquidus temperature and therefore results in a bigger liquid temperature range. This means solders with larger amounts of tin will remain in a liquid state for longer because it takes longer to cool down from 370ºC to their lower liquidus temperatures than for solders with smaller amounts of tin. This is very important!
- The 63:37 alloy is special because the liquidus and solidus temperatures are the same. This means it does not pass through a pasty state when cooling. This property is special so it has a special name – the eutectic. If you see a solder that is called eutectic then it must be this kind of solder!
So, despite what you might read elsewhere, solders don’t melt at different temperatures. We know this can not be true because they all melt at the same solidus temperature.
Maybe those people meant to say that different solders cool at different rates. Let’s consider that as an alternative possibility. First of all we need to recognise that similar metal alloys will have roughly the same thermal conductivities. We also need to remember they are a similar colour and are similarly shiny. Our scientific thoughts therefore lead us to conclude that if they conduct their heat into the surrounding glass at a similar rate when they are cooling and emit energy as heat elsewhere at roughly the same rate by black body radiation then it must be nonsense to claim that one kind of solder cools faster than another kind of solder. If the concept of black body radiation means nothing to you then read this article.
I think it’s now time to summarise the important facts about different solders:
- We expect 60:40 solder to remain liquid for longer than 50:50 solder which in turn should remain liquid for longer than 40:60 solder. It is differences in their liquidus temperatures that cause this difference.
- We also expect the eutectic 62:37 solder to change from liquid to solid without passing through a pasty state. This is because the solidus and liquidus temperatures are the same.
Before you move on to compare the two main kinds of solder we use, don’t let me stop you finding our even more about tin-lead alloys. I suggest trips to http://www.ami.ac.uk/courses/topics/0244_tsm/ and http://www.chemguide.co.uk/physical/phaseeqia/snpb.html for more information.
Comparing 60:40 with 40:60 Solder
To understand which kind of solder is best for which task we first need to summarise their differences. I will only address 60:40 and 40:60 solder because 50:50 solder is nothing more than “somewhere between”.
Here are the key facts we know about 60:40 solder
- comprises 60% tin and 40% lead
- liquid temperature range of 179°C
- shiny and bright
- stronger because there is more tin
And here are the key facts we know about 40:60 solder
- comprises 40% tin and 60% lead
- liquid temperature range of 123°C
- less shiny and not as bright
- not as strong because there is more lead
The large liquid temperature range of 60:40 solder means it stays liquid for much longer whilst cooling down compared to 40:60 solder. This means a longer working time for 60:40 solder than 40:60 solder. By “working time” I mean what we as stained glass crafters have more time to “work” with the solder when in a liquid state. It stays runny for longer when we remove the soldering iron.
The longer liquid time for 60:40 solder therefore means it is best for forming long runs of liquid solder which in turn means it is good for creating long smooth solder beads and getting nice smooth joints. No excuses for lumpy areas with 60:40 solder! For the same reason 60:40 solder is also good for “re-touching” messy areas of soldering, where new and old solder need to nicely melt together into a seamless mass and hide any evidence that a problem once existed. If you like nice smooth beautiful solder beads then 60:40 is the way to go because it’s easily available and does the best job. In theory you might get a slightly better job done with 63:37 eutectic solder – and you should now be able to say why without ever having used it!
The smaller liquid temperature range means a shorter time for 40:60 solder to remain liquid when cooling. This means it is less useful for forming nice shiny deep solder beads in copper-foiled work. It does however have an important advantage over 60:40 solder in circumstances where quickly leaving the liquid phase during cooling is desirable. The most obvious example is when you are working with lead cames. We should expect 40:60 solder to be best for soldering lead cames because we want to “get in, solder the joint and get out” quickly enough to ensure that the lead cames do not start to melt.
Another example of where 40:60 solder is particularly useful is where there is a risk of solder melting through from the front to the back of a copper-foiled panel. In my experience this tends to occur more often with 60:40 solder when large volumes of solder needs to be used to fill big holes. I will expand on this in the next paragraph to illustrate how different solders look and behave differently so should be used where they are most suited.
There are rare occasions where I use both 40:60 solder and 60:40 solder for the same joint – typically where I want to fill big gaping holes between glass globs. I start with 40:60 solder to fill the larger holes because there is a smaller liquid temperature range for 40:60 solder so it solidifies very quickly (so less chance of fall-through). I leave the joint to cool. I then quickly apply a surface layer of 60:40 solder on each side for a smoother, shinier finish. It is certainly possible to do the whole process with 60:40 with deft movements of a soldering iron but I find this hybrid method convenient and less liable to fall-through. It is also possible to only use 40:60 solder for the problems joints but I find that 40:60 solder is not as shiny.
Something else I have noticed (as have other people) is that 60:40 solder seems to form deeper and more rounded beads (that are shiny) compared with shallower (and duller) 40:60 solder beads. We like shiny copper-foiled work and habitually try to dull our lead cames so again we find that 60:40 solder is more suited to copper-foiled work and 40:60 better suited to leaded light work.
One might also speculate that 40:60 solder is more likely to corrode and darken at a rate that is closer to that of lead cames than one might expect from 60:40 solder. Another reason to use 40:60 solder on your lead cames.
The higher percentage of tin in 60:40 solder makes it stronger than 40:60 solder, in terms of tensile strength and shear strength. We also know that leaded lights have lead cames strengthened by cementing. Together one might suppose that 60:40 solder is better for strength with copper-foiled work but the truth is it is of little consequence compared to carefully designing a panel for strength. It is the cementing and not the soldering that is giving a leaded light panel its strength. For comparative purposes, consider how a weak thin panel of hardboard at the back of a self-assembly wardrobe can be so effective at maintaining the shape of a wardrobe full of clothes. It’s not strong joints, it’s the rigidity of the structure.
Incidentally, another diversion is to comment that puttying and cementing do not mean the same thing. Putty is used to fit window glass into window frames. We use a cement to cement glass to the lead in our panels. Now back to the story…
So far as I can tell, 40:60 solder is not generally available for stained glass work in the USA and 50:50 seems to have become the substitute. For that reason, and by reference to the table we looked at, I would suggest the use of 50:50 as a substitute for 40:60 solder if you cannot buy 40:60 solder simply because it is the best available alternative. Do you understand why I make this suggestion?
And, of course, I’ve yet to mention eutectic solder. Can you now predict why we would want to use it?
Recall that eutectic 63:37 solder is 63% tin and 37% lead and has the special property of going straight from liquid to solid on cooling, and back again on heating, but there is no intervening pasty temperature range. The answer to why it might be useful therefore turns out to be rather simple. The lack of a pasty phase means the solder can be changed almost instantly from solid to liquid and back again simply by applying or removing a soldering iron. With deft movements of a soldering iron it becomes possible to draw and manipulate the solder to produce textured dimensional effects. The reason I say deft is because the trick is to keep the solder temperature close to the solidus temperature so that a “blobby” lump of solder will solidify almost instantaneously. Isn’t it great that a little scientific thinking can explain how to do “decorative soldering” without having to pay someone to show you?
Another reported advantage for 63:37 solder is to bead the outside edges of copper-foiled pieces. Again, the trick would seem to be not letting the solder get too hot and runny. In truth I’ve never ever tried 63:37 solder so I’d be interested to hear of your experiences. Theory isn’t everything. Every hypothesis needs testing!
Different Solder Forms
You will find solder widely available in a solid core wire form on a spool or reel, and the amount of solder on a spool may vary. So far as I can tell, this is the only form in which solder is available in North America. Historically, this is the form used by plumbers and for electronics. In electronics they tend to use rosin-cored solder and it is nasty stuff that is not suited to stained glass work because the flux is acidic and leaves a horrible mess.
In other countries solder is also available as “blowpipe” stick. You will also find “tinman” sticks (which are more like bars) but they are rather too bulky and crude to use for stained glass crafts.
I prefer to buy my solder in the blowpipe stick form rather than on a reel. I find it more convenient to use blowpipe sticks because they are easy to handle and lighter than a reel of solder. If you can’t get blowpipe solder try cutting lengths from your reels and see why I prefer blowpipe sticks.
British Standard Classification
There is a British Standard (BS219) classification system for tin-lead alloy solders that nicely eliminates the confusion about 40:60 vs. 60:40 that I describe later.
In this particular classification system blowpipe sticks are given a letter code. It’s much easier to ask for “K stick” than “60:40 solder”, “F stick” rather than “50:50 solder” and ask for “C-stick” rather than “40:60 solder”. No scope for confusion and you are sure you’re getting what you really wanted.
Visit this UK manufacturer for more information about this classification system.
Solder Grade Availability
We know there are different grades of solder and I have already alluded to a suspicion that you can’t easily get 40:60 solder in the USA.
If you are in North America the commonly used solders in stained glass seem to be 50/50, 60/40 and 63/37. If you are elsewhere you are may to find the 40:60 alloy as well. Curiously, I could not find any reference to 40:60 solder in North American web sites (but did once spot 30:70 being mentioned in passing).
But beware. Although 60:40 solder ought to mean an alloy of 60% tin with 40% lead, some people (and some suppliers) get confused and inadvertently reverse the numbers. If you have any doubts ask them “does your 60:40 solder contain 60% tin or 60% lead?” and if you can’t get a sensible answer try looking at the price – higher proportions of tin result in higher solder prices because tin is always more expensive than lead as a raw material.
Lead and Purity
You will find comments in various places on the Internet that tell you to look for solders that are “free of impurities” in the component metals. You will also find comments that warn you that impurities cause a “scum” on your solder beads, that they degrade soldering iron tips, and interfere with the proper reaction of patina chemicals resulting in undesired finishes. You will also find advice that tells you to insist on lead and solder that comes from virgin lead, meaning not recycled. And finally, you will see comments about one brand of solder being better than another because it doesn’t make use of recycled materials.
If you look here you will discover that lead has one of the highest recycling rates of all materials in common use today. Recycling rates of 100% are achieved in some countries and others are not far behind. So the chance of finding lead cames and solders containing only virgin lead is rather optimistic. All that we need to do is be vigilant and not buy dodgy solder from dodgy suppliers.
I am dubious about the claim that some solders degrade soldering iron bits. The only significant causes of soldering iron bit degradation I am aware of are over-use of soldering iron tip cleaning materials (such as sal ammoniac), the use of acidic fluxes and the long-term use of damaged tips.
I doubt the claim that some solders interfere with patination chemical processes. Patination chemicals react with the lead and the tin in the solder so all that the patination chemical needs to find on the surface of a solder bead is tin and lead to produce their surface effects. Only if the soldered surface is not clean or the solder is massively contaminated can I see this problem arising.
Comments about impurities in solder causing a “scum” on solder beads I find hard to believe and I have neither seen nor heard any tangible or verifiable evidence for it. I have certainly seen impurities causing a scum on solder but they have washed away on cleaning and are more likely to have originated as lead and tin oxides that have naturally developed on old lead cames, muck from a dirty soldering iron, zinc from safety flux, muck on copper foil or maybe even copper compounds from old copper foil.
It is however worth mentioning that some solders, not intended for stained glass use, may contain other metals in their alloy. Be sure to avoid anything containing cadmium, antimony, or other really nasty elements. Not that I’m saying lead is particularly healthy!
A slight detour into solder fluxes for use with solders is perhaps useful.
Fluxes are materials that help us join one kind of metal to another. There are many fluxes and many kinds of metal. The important this is that we use the right kinds of fluxes for the metals we are using and avoid the ones that might cause us problems.
The first important thing to remember is to never ever use rosin cored solder or rosin as a flux. Notice the word “rosin” because it is not the same as “resin” as some people might suggest. Rosin cored solder is used widely in the electronics industry. The rosin core is acidic and leaves the brown resinous deposit you might have seen on a circuit board. It also produces a nasty vapour which can sometimes be seen as a white powdery deposit. If you try to use rosin as a flux, or rosin cored solder for stained glass work you will be left with a mess that is not easy to clean off.
I doubt I am telling you anything you don’t already know, but 40:60 solder is best used with tallow as a flux and 60:40 solder is best used with a non-acidic safety flux.
Tallow is an interesting old substance – it is derived from animal fats so I guess vegans might not want to use it. This in turn makes me wonder whether a leaded panel is a suitable gift (or purchase) for a vegan.
If you want to make your own safety flux then look here for more details. It’s easy, cheap and exactly the same as many commercial formulations.
There is no difference between different kinds of solder in terms of how well they take patina. What really is important is the thorough cleaning and preparation of soldered panel in anticipation of patination.
If you need to make your own copper patina or want to know how it works, look at this article.
Choose Performance, Not Price
So, it’s finally time to pull all the information together and reach some rational conclusions about why to choose one kind of solder over another for a particular purpose. It’s time to summarise.
The cost of each grade of solder depends on the relative amounts of tin an lead in the alloy because the underlying prices of lead and tin are very different. So, the price depends on what’s in the solder and does not imply anything about performance or behaviour. Nearly all the lead we use is recycled so trying to find solder made from virgin lead is optimistic. Buy a reputable brand from a reputable supplier if you are concerned about the quality and performance of your solder.
Choosing a grade of solder ought to be based on how it behaves and how it performs if craftsmanship is your primary concern. You should not be choosing a grade of solder on the basis of price unless you are cash-strapped and are prepared to compromise on the quality of your work.
These are what I believe to be rational reasons to choose each common grade of solder:
- The 40:60 solder is best suited for work with lead cames because it stays liquid for a short time when cooling and produces duller results than 60:40 solder. It can also be useful for copper-foiled work to reduce the chance of fall-through when bridging large gaps.
- The 60:40 solder is best suited for copper-foiled work because it stays liquid for a long time when cooling and can produce smoother and shinier beads.
- The 50:50 solder is a compromise if you cannot buy 40:60 solder. It is not as good as 60:40 solder for copper-foiled work because it does not stay liquid for as long.
- Eutectic 63:37 solder may be useful for fancy decorative soldering work because it will instantly solidify during cooling without passing through a pasty stage.
And finally, only ever use a suitable flux. There are many commercial varieties of safety flux that are suitable but the recipe I give you here for copper-foiled work is cheap and as good as the competition. Use tallow for leaded panels if you are not a devout vegan. Never use rosin as a flux, or rosin cored solder.
For more information about solder, visit http://en.wikipedia.org/wiki/Solder. For a alternative source of good information about solder, as well as copper foil and other related products visit http://www.inlandcraft.com/howto/pdf/htsold.pdf – but do bear in mind it’s in their interests to promote their own products. Other products and suppliers do exist!