Etching and Engraving Dichroic Glass

Photo-0003 Etched & Engraved BlogWhilst browsing around the Internet recently I encountered comments about etching dichroic glass. I found plenty of vague and conflicting comments about what to do and what to expect.

So today’s posting is about some experiments I have been doing. I hope it leaves you with a clearer understanding of what you can do and what to expect.

If you’re a regular reader of my blogs you will realise that you don’t get away without some science somewhere or other in my postings. The connection I want you to make on this occasion is that dichroic glass works in exactly the same way as a droplet of oil on water, the wings of a butterfly or the carapace or a beetle. They all produce vibrant colours when, in fact, there is no pigment or dye producing those colours. The underlying physics is thin film light interference. If you’re interested learn how colour can come from something colourless then I recommend a visit to http://www.webexhibits.org/causesofcolor/15.html and http://www.physicsclassroom.com/class/light/Lesson-1/Thin-Film-Interference for more information. You may also find it interesting and informative to visit http://en.wikipedia.org/wiki/Glass_etching for some general background reading about etching and engraving methods.

As far as my own experiments are concerned I have tried two basic techniques – etching and engraving. The difference between them is that etching is a chemical process whereas engraving is an abrasive process, each of them aiming to strip away a very thin metallic layer from dichroic glass. With reference to the picture I will describe each method in turn.

There is no reason why you should not try this even if you only have a little microwave kiln.

Etching Dichro

The dangers associated with hydrofluoric acid are well known and it takes a brave person to work with this particular acid. Despite what you might have heard, hydrofluouric acid can be obtained in the UK, from places such as APC Pure (at https://www.apcpure.com/). I mention APC Pure simply because they also supply a variety of other products that happen to be useful for glass workers but do not charge daft prices that you’ll find at most stained glass suppliers. Examples are acetone and isopropanol (for cleaning glass), copper sulphate pentahydrate (to make copper patina), wash bottles, buckets, bottles and jars. Other than being a customer, I’m not connected to APC Pure.

But I digress. Back to etching…

For small-scale gentle acid etching there are several brands of glass etching cream. An oft cited brand is Armour Etch. These creams are relatively safe and easy to use even though their underlying chemistry is no different than hydrofluoric acid. The difference is that the creams are very much weaker than hydrofluoric acid.

I tend to use a paintbrush, cotton bud or a plastic sponge to apply glass etching cream. When I remember, I use cheap plastic disposable gloves to protect my hands. Only if you are a messy worker should you consider additional precautions.

I have found that the metal coating of some kinds of dichroic glass will etch away completely in a matter of seconds whereas others can take 20 or even 30 minutes to etch away completely. It is only by experimenting that you will discover what to expect. My suspicion is that some types of dichroic glass have a protective glass layer on top of the metallic coating but some do not, that some metal coatings will be thicker (or thinner) and that some metal coatings are more susceptible to acid etching than others (eg see Reactivity Series at Wikipedia). It is certainly the case that CBS Dichroic (at http://www.cbs-dichroic.com/faq.asp) mention that their standard colours have half the number of metallic layers than their premium colours as well as saying they apply a quartz crystal protective layer. The results of etching dichroic glass will therefore depend on all these factors.

To stop the etching process is easy. You can optionally begin by wiping away excess etching cream with a paper towel. The important step is  immersing and cleaning the glass piece in water. If the etching cream is not cleaned away completely then it will continue to etch the glass.

In the top right of the picture you will see four small oblong panels that took only seconds to reach a state in which some metallised areas are partially etched away and other areas have no metal coating whatsoever. I used a small paint brush to apply the etching cream and almost immediately washed away the etching cream, repeating the process if necessary. Evidently these dichroic glass had little or no protective quartz above the metallisation and/or had fewer or more reactive metallic layers.

The results are rather interesting in that the degree of processing results in different colours, or black if the metallic layer is completely etched away. The reason for different colours can be related back to an expectation that light interference will change when the dichroic layer is partially etched away.

Below and to the left of those four small oblong panels are examples where the etching was very slow, resulting in nothing more than subtle colour changes. The blue finger to the left has also been engraved to enhance the colour change effect.

To the left of the blue finger are two pieces of dichroic glass, one with a floral pattern and the other with a starry pattern. For both these examples two craft paper punches were used to stamp out self-adhesive plastic shapes that have been applied to the dichroic glass to act as an etching resist. This particular colour of dichroic glass took a looooong time to etch. If you look very closely at these two pieces you will see that the black areas do still have a little of the original dichroic coating remaining – and it is the same colour. I love the starry example as the feint wispy effect gives the impression of a starry sky with wispy clouds.

The last remaining example of etching is in the middle of the picture, where bands of varying width have been etched away. This could also be done by engraving.

What I want you to realise is that etching can be used to change a plain single-coloured dichroic glass into a multi-coloured dichroic glass.

Engraving Dichro

Examples of engraved dichroic glass can be seen mostly to the left and at the bottom of the picture. The finger of glass at the bottom left of the picture is the exception because it is engraved iridised glass – a hint that you can also engrave iridised glass!

The purpose of the experiments was to see how different line widths and different types of patterning would turn out. I was not out to impress you with artistry.

Dots, squiggles, thin lines, thick lines, regular patterns, irregular patterns. They all seem to lift a boring piece of plain dichroic glass into something more interesting.

I am particularly fond of the two colourful oblong pieces towards the lower left of the picture where fine engraved lines have been used to allude to the contour lines and colours of a map.

It is a simple process to engrave dichroic glass. You will need a light and comfortable hand-held electric drill (such as from Dremel) and some diamond coated burrs. You may also find it useful to consider a “flexible shaft”, particularly if you find handling a drill too heavy and cumbersome.

The type of diamond coated burrs I find most useful have a spherical ball-shaped tip because it’s easier to use them. They grind away the same width of line no matter how you’re holding the drill or in which direction you are travelling. Different diameter ball-shaped burrs produce different line widths.

It is also possible to adjust a line width by applying more (or less) pressure but resist the temptation to apply more pressure because it will shorten the life of your diamond burrs. Better is to change to a different sized burr.

The reason to use water (or oil) lubrication with diamond tipped burrs is mostly about keeping the diamond grits cool and washing away abrasive waste materials – the objective is therefore to extend the life of the burrs. Also important is to recognise that the diamond grit coating will be stripped away due to friction if more than a light touch is used. This is why you get told to let the diamonds do the work and are told not to hurry the process by applying pressure.

But you will see from the examples that we only need to scratch away a few thousandths of an inch of dichroic coating over a small area of glass. This means the diamond grit coating will not get too hot. Not unless you are applying pressure and trying to hurry the process. In turn, this means heat caused by friction should not become a problem, just as large amounts of abrasive grinding waste will not be a problem. Therefore, it is OK to engrave without the use of water or oil. But beware the dust thrown up by dry-engraving glass and use a respirator if you want to avoid silicosis.

Finishing Off

At the end of your work session you will find that everything you have etched and engraved will have a dull-black surface caused by the etching and abrading. This can be resolved by fire polishing (as shown by the various circular and finger shapes in the picture) or by capping with clear glass (as shown by the various rectangle shapes in the picture).

Remember to dispose of etching cream laden paper towels and other waste materials carefully. Also thoroughly clean your brushes or the acid will continue to etch any metals they come into contact with.

Some Conclusions

Different kinds of dichroic glass will behave differently when a glass etching cream is used. Armour Etch is an oft quoted brand but there are several others that also do the same job. Glass etching creams work in the same way as hydrofluoric acid but are much safer and easier to use.

Some kinds of dichroic glass metallic surfaces will etch away very quickly but some will take a long time. It is in the nature of how a particular piece of dichroic glass has been made that causes this difference so pre-testing small scraps of dichroic glass is the key to discovering how fast a particular dichroic glass will etch.

Partially etching plain dichroic glass, using a brush stroke or cotton bud smear will result in a multi-coloured dichroic effect that depends on the degree to which the surface gets etched. Rinsing and cleaning the glass piece in water will stop the etching process immediately. The colour changes in a partially etched surface are the result of light interfering in a different way. Although difficult to control and predict, it is a novel way to change plain dichroic glass into something unique and interesting.

When “resistant” dichroic glass is being etched, it is more easily possible to stop the etching process at a desired state. It is possible to cause only subtle colour changes across the surface, which can be made more exciting by engraving contours around the different coloured areas.

Self-adhesive plastic can be applied to the dichroic glass surface to resist the etching process so that neat well-defined shapes and patterns can be produced for decorative effect. It is also possible to stop the etching process just before the whole dichroic coating has been removed from unprotected areas, at which point there will be a wispy patchy effect. This has been illustrated by the “starry sky” example.

Engraving dichroic glass can be achieved with a hand-held electric drill and diamond coated burrs, ball-shaped burrs perhaps being the easiest to use. Lines engraved away from the dichroic coating can be made thicker and thinner by using different diameter burrs. With due care and consideration dry engraving is a suitable method.

A fire polish or capping with clear glass is necessary to return etched and engraved glass surfaces back to a glossy state.

That’s all. Your turn to experiment!

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About chatterglass

Maker of stained glass frippery.
This entry was posted in Dichroic Glass, Engraved Glass, Etched Glass, Experiment, Microwave kiln and tagged , , , , , , . Bookmark the permalink.

3 Responses to Etching and Engraving Dichroic Glass

  1. RJ Barr says:

    Thank you for some really interesting articles. They have been very instructive.
    I found this site while googling ‘cream etching iridised glass’ . Can you tell me the difference between dichroic and iridised glass? is it possible to cream etch iridised glass?
    Thanks again for a great site.
    Ruth

  2. chatterglass says:

    First of all, many thanks for your kind words Ruth. They reassure me that I’m not wasting my time.

    Dichroic and iridised glass similarities and differences relate both to what they are and how they are made. Both have metals deposited on the surface of glass and both cause the light interference colours that are so lovely. The difference comes from how the metals are deposited. The essence of the difference is that iridised glass is relatively easy to make using hot glass and metal vapours in the air by a method that is not very well controlled (so is a “Victorian artisan technology”) whereas making dichroic glass uses cold glass and metal vapours in a vacuum by a method that is highly controlled (so is a “space age technology”). Have a look at http://www.cmog.org/video/making-iridized-glass and compare with what you see and read at the CBS dichroic site.

    Until this evening I had not etched or engraved iridised glass so, for you, I did a quick experiment with two different scraps. They both were as easy to engrave but etching took much longer. Sadly, the iridised coating entirely etched away in blotchy patches rather than change colours like happens with dichroic glass.

    Based on this experiment, and an observation that it’s easy to scratch a dichroic layer, but not at all easy with iridised glass leads, and the difference between how they’re made, I am led to suspect that the iridised metal layer is thicker and maybe at least partially fused into the glass whereas the dichoic layers seem to be very thin and entirely on the surface of the glass (but sometimes with a very fine quartz protective layer).

    I’ve made a note to look again in more detail over the coming dark winter months. If I discover anything new I’ll do an article about it.

  3. RJ Barr says:

    Thank you for a very thorough reply and the link on making iridised glass. Both were very informative. I had not realised how expensive dichroic was till I looked on the CBS site, I expect most people only use small amounts in fusing, which I havn’t tried yet.
    Thanks again.
    Ruth

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