I did plan to write about glass cutters but got side-tracked by comments relating to”cutting oil” and suggested alternative whilst browsing around on the Internet. I promise to come back to glass cutters at some future date.
Sorry, but there are no exciting pictures of cutting oil in today’s blog posting!
Who’s Using What and Why
After meandering around the Internet I found a wide variety of liquids being used with glass cutters. Some of the places I visited include the Stained glass Town Square forum where you will find a discussion that caused me to make this blog, a comment in the Dendroboard forum, some good, bad and ugly advice all in one place at Stained Glass Town Square (again) and the typically dodgy advice and guidance at Yahoo Answers. I encourage you to search for more.
As one commentator points out, “Professional glaziers have been dipping their cutters into oil for over a century” so we can assume that there must be some rational reason for using a lubricant when cutting glass. A completely plausible explanation for kerosene being the traditional “cutting oil” is that “back before electric soldering irons, a glazier would use a kerosene lamp to heat the soldering irons, so there was always a supply of kerosene handy in the studio.”
Although kerosene evaporates cleanly and doesn’t gum up a glass cutter it does have the problem of producing a persistent odour that can cause nausea and headaches for some people.
Commercially-made “cutting oil” is very popular and seems to come in two distinct forms – either a mineral oil or a water-soluble formulation. I’ll talk about them both, in turn.
The “usual” cutting oil that you may have purchased from a stained glass suppler is probably nothing more than white mineral oil according to the MSDS information I’ve looked at. The term “white mineral oil” is deliberately vague and is synonymous with both “light petroleum distillates” and “heavy petroleum distillates”. This means you’ve been buying something that is paraffin at the heavier end of the scale, tending towards kerosene at the lighter end of the scale. If you remember your High School chemistry then you may recall fractional distillation as being the method by which these mineral oils are produced from crude oil. If you’re really “on the ball” you may also remember catalytic cracking as well!
Therefore, any petroleum-based oil with a viscosity that is “about the same” as “white mineral oil” is a rational and reasonable substitute for commercial “cutting oil”. At the heavier end of the scale is the likes of 3-in-1 oil, which does appear to be used by some people, though this strikes me as being rather viscous. This observation seems to be supported by someone else using 3-in-1 oil who says they add some “Varsol” (what ever that might be) to thin the oil. Heading down the scale of viscosity are people using mixtures containing paraffin (not so viscous) and kerosene (least viscous) in products such as tiki-torch fuel. Other “light oil” products being used that are very similar include sewing machine oil, bicycle chain oil, lamp oil and baby oil.
All this might explain why people who prefer kerosene will also suggest that “cutting oil” is too viscous and does not wick properly in oil-filled cutters. However, other people complain about their cutters leaking which suggests the exact opposite. My guess is that the problem is not only the cutting oil but the condition and “brand” of the cutting head – I have never had a problem with leaking Toyo cutters but do with a cheap Chinese equivalent.
There is also a synthetic lubricant being sold. It is supposed to be water soluble and “environmentally friendly”. Apparently it washes away easily with water so that your copper foil will stick better. So far as I noticed on the Internet, nobody said that used this kind of lubricant. The manufacturers safety data sheet (MSDS) reveals a formulation based on ethylene glycol, diethylene glycol and water. This explains why it is water soluble.
There are also a few “unusual” choices. WD40 is mentioned by one person and water is mentioned by another. Although water might seem strange, it is implicitly involved in the “rubbing” of spit into score lines by some people (more about this later) and is contained in the newer “environmentally friendly” cutting liquid. Vegetable oils (such soya or corn/maize) have also been used though there are warnings about “gumming up” being a potential problem.
Last, but not least is the use of nothing at all as a lubrication. A fair number of glass workers seem to use glass cutters without any form of lubricant, sometimes giving a rational reason for doing so (such as keeping the glass clean) but often the justification is absent or irrational.
Are you Dipping or Wicking?
Oil-filled cutters are a relatively recent invention and are very popular. They have a little wick inside to slowly “feed” the cutting wheel with lubricant.
Oil-filled cutters can be contrasted with their predecessors which were not oil-filled. Many of these “more primitive” cutters are still bought and used because they tend to be cheaper than oil-filled cutters. With these older glass cutters the method of lubricating the cutting wheel is called “dipping” and it means you dip your glass cutter’s cutting head into a jar containing your chosen lubricant, perhaps with some rag or wadding at the bottom of the jar. Many people who are “dippers” seem to be “traditionalists” and use kerosene.
Generally speaking I tend to use an oil-filled glass cutter containing “cutting oil” but there are occasions when I find myself with a more traditional glass cutter closer to hand. Rather than dipping a traditional cutter into a jar I use a shallow tin (with a hinged lid) that contains a few layers of old denim rags heavily soaked in cutting oil. I replace the rags from time to time as glass particles accumulate. Having a shallow tin with a hinged lid is handy because it does not leak when transported “off site”.
Although it may not yet be apparent, there are justifiable reasons to use one kind of lubricant in an oil-filled cutter but a different kind when dipping. For example, some people suggest that “cutter oil” is much too viscous to wick properly in an oil-filled glass cutter and suggest that it is therefore only suitable for dipping.
Good Cutter Lubricant Characteristics
Here is my candidate list of characteristics that may be important when comparing one “cutter oil” or other lubricant with another. The relative priority of these characteristics will depend on personal preferences as well as technical considerations – for which words like “appropriate” are deliberately vague. You might choose to make your own list and ignore mine.
- Remains liquid at room temperatures (and relates to appropriate viscosity);
- Will not thicken or chemically degrade over time (eg “oxidative stability”);
- Ability to biodegrade and “save the planet”;
- Will not corrode the metal parts of a glass cutter;
- Appropriate evaporation rate (which can also relate to noxious vapours);
- Residues evaporate or burn away cleanly (for fused glass work); and
- Residues are easily washed or wiped away (for copper foiled work).
You will find some alternative perspectives within the online discussion here.
An appropriate viscosity depends on how you are using your “cutter oil” and at least to some extent is a matter of personal preference. It also depends on the “leakiness” of the cutter head. And there are several commentators thay say that we must ensure our oil-filled cutter can effectively “wick” the oil and that it must be less viscous that we might use when dipping a glass cutter. This distinction here would be paraffin vs. kerosene, or a mixture of them both.
Lubricants that chemically degrade will have a limited shelf-life so stability is important. One mechanism by which some oils degrade is by slowly oxidising and in the case of vegetable oils this can be spotted both in terms of the increased viscosity and also the rancid smell. So, if a lubricant is susceptible to oxidation then the process causes the lubricant to progressively thicken and it will ultimately reach a point where it will “gum up”. This will be a problem for oil-filled glass cutters and remediation of the “mess” is going to be more difficult.
The ability to bio-degrade and other environmental concerns should be balanced against a recognition that we will do not use large quantities of which ever lubricant we choose. In the broader context of “environmental concern” we should also recognise the far larger environmental damage caused by putting whatever lubricant we might choose to use (even the “environmentally friendly” ones) into a plastic bottle, packing and shipping it around the world and let’s not forget the final step of the environmental damage caused by us just “popping out” in our car to buy the darned stuff!
Some choices for “cutting oil” are smelly and can evaporate quite quickly. Working in a confined space can be a problem with any volatile substance. Bear in mind that vapours causing headaches are not always the most serious concern with a volatile liquid product so do remember to ask your supplier for the Manufacturer’s Safety Data Sheet (MSDS) or hunt them down on the Internet. If you are an employer then asking for MSDS information for all your chemical products should be part of your Health & Safety management routine.
Some people eschew the use of cutting oil and all other lubricants, choosing to score glass with a dry cutting wheel. Sometimes there may be a rational basis for the decision though many point out that the life of a cutting wheel and the quality of a score can affected detrimentally – something that I will consider and question later.
With a list of desirable lubricant properties and examples of what people are using it’s time to give some rational thought to asking why the scoring process might need some kind of lubricant. We will first look at the scoring and healing processes within glass for one perspective and then look at the relative hardness of cutter wheels and glass as another perspective.
Scoring and Healing
Many people, like myself, subjectively believe that “old scores” seem to be harder to break than a fresh score and the commonly held belief is that there is a “healing” process that takes place very slowly within the glass. But, as is usual within stained glass crafts, it is always possible to find someone with an unevidenced and unjustifiable polar opposite opinion such as this one: “Glass doesn’t heal. That’s a myth.”
Is it perhaps the conflicting and sometimes irrational hearsay, magic and mysticism that I encounter in stained glass crafts that causes me to do these blog postings? Hmm. Probably.
To complicate matters further, I see that many people believe that using a lubricating oil when scoring results in a better break – yet some believe a dry score is better. More mysticism, magic and hearsay to deal with.
Let’s see if some science and rational thought can help us find meaningful answers. We need a plausible explanation for why glass scored with a lubricant might be improved. It should also explain why “old scores” might be harder to break. With such information we are in a better position to choose the best “cutter oil” for our glass cutters and dismiss some more of the myths, magic and hearsay you’ll encounter on the Internet.
My curiosity was aroused by a visit to this strange article about glass cutting where a claim is made that alkaline substances that contain hydroxyl ions, such as spit, will help with glass scoring. An interesting idea but suspicious because I know that spit can be acidic (after eating) as well as alkaline (after tooth brushing). Also, the oft-mentioned assertion that “Glass is a super cooled liquid” in this source causes me to be extra suspicious because although the atomic structure of glass resembled what can be observed in any supercooled liquid phase, glass displays all the mechanical properties of a solid. OK, I see you yawning… Put simply, glass is an amorphous crystalline solid, not a liquid. More about this at Wikipedia in case you’re interested.
But I then found a more reliable source via this page which contains a link to a YouTube video which in turn cites a Spectrum Glass article that cites the Scientific American journal as a source. I was unable to find the original Scientific American source but did at least find the Spectrum Glass source.
The Spectrum Glass article tells us that “water causes glass to crack more easily because when a water molecule enters the crack, a reaction occurs in which a silicon-oxygen bond at the crack and an oxygen-hydrogen bond in the water are cleaved, creating two hydroxyl groups attached to silicon. As a result, the length of the crack grows by the size of one bond rupture. The water reaction reduces the energy necessary to break the silicon-oxygen bonds, thus the crack grows faster.”
So, it is the ability to produce hydroxyl ions, rather than being an alkaline substance, that explains how bonds are “helped” to cleave by the use of water. And I note that spit contains water. This all seems to be plausible but I can’t find any explicit information relating to the “healing” process or the use of oil so I’ll have to some inferring and this means I might be wrong. You can decide for yourself…
My first thought is that mineral oils might also assist with the same crack-forming process but with a subtle difference because mineral oils contain no water and therefore can not produce hydroxyl groups. This leads me to suggest that what’s most important is that oil gets into a glass rupture in exactly the same way that water does. But, unlike the water situation, the physical presence of the oil rather than a chemical change is the barrier to the re-establishment of silicon-oxygen bonds that have just been ruptured. We therefore have a plausible mechanism that I hope correctly explains why oils will also assist with the crack-forming and maintenance process. This is alluded to by at least one commentator on the Internet so may indeed be correct.
My next thought is that is reasonable to assume that any water within the score line fracture will eventually escape and evaporate away, leaving a “dried out” crack. It is also reasonable to assume that the same thing will happen with mineral oils and other liquids, though not necessarily at the same rate as might happen with water. My suggestion is that the silicon-oxygen bonds in a dried-out crack will be able to re-form and “heal” the crack at least to some degree, albeit slowly. We therefore have a plausible mechanism that I hope correctly explains the long-term “healing” effect.
In conclusion, we now have rational explanations for why a fluid can help the crack-forming process and for the “healing” effect. We therefore have a rational justification to use a water-based or oil-based cutting fluid rather than to use dry scoring as a normal practise.
Thinking About Hardness
Many people, like myself, subjectively believe that cutting oils (or whatever) will lengthen the life of a glass cutter’s wheel. Glass is hard and metals are soft. It all seems so obvious.
But once again, heresay, magic and mysticism rules, rather than rational thought and science. We need to look closer and think harder.
To understand whether or not a glass cutter’s wheel gets “ground down” by fragments of glass requires some understanding of how “hard” the materials are, for which there are many “scales” of measurement. Perhaps the best-known and popular measure is the Mohs scale of hardness. You can visit here and here for more information about the Mohs scale and hardness.
The Mohs scale has smaller numbers for softer materials and larger numbers for harder materials. This means a harder material can “scratch” something of equal or lower hardness.
Here are some hardness measures on the Mohs scale:
- 4.0 to 4.5 steel (cheap wheel cutters)
- 5.5 to 6.5 glass (soda glass tends to be quite soft)
- 9 tungsten carbide (posh wheel cutters)
- 9 sapphire (cheaper very old-fashioned cutters)
- 10 diamond (posh very old-fashioned cutters)
So, for example, a diamond will easily scratch any kind of glass. This much is common knowledge.
More important to us is a confirmation that glass will scratch and abrade a steel cutting wheel. But I hope you can also see that glass will not scratch or abrade a tungsten carbide cutting wheel.
So, these discoveries mean that the life-lengthening effect of using a cutting oil definitely holds true for steel cutting wheels but does not appear to be true for tungsten carbide cutting wheels. If there is any rational reason to use a cutting oil with a tungsten carbide cutting wheel then it’s not related to the hardness of glass. This brings into question the commonly-held view that cutting oil lengthens the life of our (tungsten carbide) cutting wheels.
To end this section I leave you with a tricky question, or perhaps I should say a trick question… If steel is softer than glass then how does a steel cutting wheel manage to produce a usable score line in glass?
Reasons to Lubricate, Or Not
If you’re still reading and haven’t yet fallen asleep with boredom, you’ll begin to understand that comments such as “oil helps you see where you have scored” and also “with light pressure, no oil is needed” are of limited value and need clarifying and justifying before acceptance.
So, I think we are now in a position to make two lists with which decide whether or not to use a lubricant with our glass cutters. Here are my suggestions but you might make different lists:
Reasons to lubricate:
- Lubricating the cutting wheel keeps it spinning freely and smoothly.
- Free up any shards of glass that could get stuck in the cutting head assembly.
- May help to preserves the cutting wheel edge (if stainless steel) by washing away glass particles.
- Prevents shards of glass from flying around.
- Keeps the scored line open and slows down the “healing” process.
- Heat generated by the scoring process is dissipated.
- A trail of lubricant helps to make feint score lines more visible
Reasons not to lubricate
- Tungsten carbide cutting wheels are harder than glass
- Lubricants make a mess that needs to be cleaned away before copper foiling or kiln firing.
I can’t make the choice for you but my inclination is to use a lubricant, especially when using a steel wheel, but not worry so much if I’m using a tungsten carbide wheel.
Choosing What and Why
Now that we’ve done some “hard thinking” and decided whether or not to lubricate we’re in a position to make sense of the choices available to us.
Dry Cutting has an advantage when copper foiling because the copper foil’s adhesive will better adhere to glass if there is no oily deposit. The alternative is to wash or scrupulously wipe the glass pieces.
Whether or not dry cutting is an advantage for kiln firing glass is questionable. I say this there’s lots of opinion, and I suspect a lot of irrational paranoia, but little basis in testable facts on issues relating to contaminants (even fingerprints) causing devitrification. Here are a couple of comments to consider and contrast… A clean cutting oil is a simple hydrocarbon mixture which will cleanly evaporate or”burn off” within a kiln – but we are told this can cause devitrification. However the use of other “contaminants” such as Glastac or White Glue (PVA) are routinely used and also “burn off” – but we are told these are not a risk for devitrification. This all looks rather self-inconsistent to me. We want facts not superstition and hearsay!
Dry cutting with steel wheeled glass cutters is a bad idea because glass particles are harder than steel. However, tungsten carbide wheels are harder than glass so dry cutting ought to be OK with these cutters.
Vegetable oils are very cheap and abundant, they have a low odour, evaporate slowly and are biodegradable so they have good environmental credentials. However, they have a rather high viscosity that increases as the oil slowly oxidises and turns rancid, causing a cutter to get “gummed up”. A conclusion for vegetable oils is that they should only be used in an emergency, but if you really are in this situation then would be perhaps be better to siphon-off a little petrol or diesel from a car instead if you can cope with the odour?
Mineral oils based on kerosene, paraffin and mixtures of them are our current favourites. They are also the basis for commercial products. Kerosene is lighter but more volatile and more likely to cause a lingering odour and cause headaches but some believe paraffin is a little to viscous. Either way they are being used in small quantities so perhaps the environmental problem of them not being biodegradable is not such a major consideration.
More to the point, if you want to “save the planet” you should also be concerned when buying an “environmentally friendly” alternative. Do we not do more environmental damage by putting it into a plastic bottle, shipping it and then going to SGC supplier in the car to buy it?
The prospect for using water or a modern water-based “environmentally friendly” formulation is worth considering because they can be wiped away or washed off and leave no residue. It is certainly a reason to consider them for copper-foiled work and for kiln work but the reservations I have for dry cutting should also apply here as well. Another concern is whether water and water-based formulations might slowly corrode or oxidise the wheel and spindle of a glass cutter. I can not tell you if this happens because I’ve not use these formulations.
Make Your Own Formulation
Formulating your own “cutting oil” based on mineral oils is easy but to produce your own “environmentally friendly” is another matter.
From what you’ve read you’ll realise that “mineral oils” come in many disguises, such as sewing machine oil, baby oil, kerosene and paraffin. They’re all the same but slightly different. This means you easily formulate your own cutting oils by mixing them to get the right odour, viscosity and so forth.
I have inherited enough “cutting oil” to last a lifetime so I’m unlikely to experiment in this area. Sorry. This time you can lead and I’ll follow!
Over and Out
I hope you found this useful even though I got truly distracted from my original intention to write about glass cutters!