Rounding off the edges.

Never a big fan of edges where rounded curves are sexier :-)

With that in mind I'm contemplating rounding off the edges and corners of my black wooden EW case.
Not a huge problem woodwork wise but when i come to re-coating it in black, what kind of paint is best to use and will I have to do a major retune?
Roy

Hello Roy,

I will mention that using Rust-oleum gloss black lacquer has a terrible effect on theremin operation when the pc board is mounted within 1/4" or 6 mm of a painted wood surface. Something in the paint must be conductive or inductive. Painting the entire outside of the enclosure with this can of stuff would concern me.

I just check it and the painted wood does not reveal itself as conductive at all, it must be something else?

Christopher

I see an EW and I want it painted black (and the edges rounded off).

Hello Roy,

Any paint containing conductive particles of any kind (and for black, these are likely to be carbon in some form) will affect capacitance - even if the paint itself isn't conductive.

Paint only becomes measurably 'conductive' if conductive particles touch each other or are close enough and of the right structure to enable quantum tunneling.. But each conductive particle will have capacitive coupling to the circuit, and capacitively couple to other particles (and edge effects / capacitive fringing can make this inter-particle coupling extremely strong - strong enough that a painted surface can behave nearly like a sheet of conductive or metal foil)

So, no conductive particles of any kind in the paint! - And measuring the conductivity of the paint isnt going to give any clue about its suitability - you need to get a data sheet and study the chemical composition! (and finding such data isnt easy)

While on this subject, the above properties can be useful! Mix graphite powder and / or magnetite powder with glue, and one gets really useful paint for shielding e-fields.. Use magnetite, and one also dissipates magnetic fields!

(I think it was you who advised me about magnetite, when I was asking about using ferric oxide - Magnetite is much better!)

Fred.

One could probably test paint suitability by painting a sheet of paper and sticking this to a theremin antenna - paint that increases capacitance will probably cause an increase in audio pitch if you do this... But its probably easier to use some color other than black! ;-)

"I see an EW and I want it painted black (and the edges rounded off)." - Dewster

Shouldent that be..

"I see an Ether-Wave and want it painted black.." singing "I want an ew and want it painted black" could be misconstrued as abusive to ewes. ;-) ... (particularly the " edges rounded off ")

Thanks folks for the replies.

Fred, the spooky thing is that the coating can show no conductance and yet have an effect due to capacitance, which makes the coating choice doubly difficult!

I had a sneaky suspicion that all things of a black paint nature had a certain amount of carbon in them and so up to a point would be conductive and probably have a significant effect on the tuning of the instrument.

An alternative would be to sand the whole of the case down to unstained wood and rub all over with Danish oil-would give it a nice polished wood finish but then again REMOVING all of that blackness put on by MOOG in the first place might also have a significant effect on the tuning.

Another would be to round the corners and leave it two tone (all Ska and Specials vid links most welcome!).

So many options!

Oh and dewster, doesn't Mick look young!

ehhh...and I do believe it was me who gave you the tip off about Magnetite Fred :-)

Roy,

I am fairly sure there are carbon-free black colourings in some paints - Might be worth asking Moog what paint they use ?

Fred.

Yo Fred!

Contacting Moog had occured to me but I thought I'd ask here at the fount of all theremin knowledge-and I mean that in the best possible way!

Black shoe polish (unscrupulous fiddle repair people use shoe polish to 'antique' fresh repairs) or bitumen are also on my radar...

It seems to me that the finish on the black EW is more of a stain than a varnish or paint as it seems to be pretty thin, which means that it would have to be fairly opaque in it's un-applied state.

Aye, ok, I know it's only a cosmetic thing but it's still a thing!

I mean, for goodness sake, Moog do a green fluorescent version and I'm sure they do it at least expense, ie, nae change tae the guts of the beastie...

:-)

R

Ok - There are these large black felt-tipped pens with alcohol solvent.. They are really dark, and the ink dries permanent.. I am not a chemist ;-) but suspect the pigment isnt carbon based... There is also the Sharpie markers, and I would be surprised if their pigment was carbon..

Is there some reagent with which one can test for carbon? I remember as a kid playing with dangerous chemicals (Benzine, mercury, bromine, carbon-tet, trichloretylene - to name a few) and seem to remember bromine doing strange things to my pencils graphite... (I was also fascinated by passing currents through different mixtures, watching an egg white go green for example - I now suspect it was more due to the copper wire though..;-)

If you can get a simple chemical, and test a Sharpie, that might be the easiest....

If you do find a suitable blackness, (and survive the experiment) please let us know!

;-)

Fred

ps - phosphorescence is really interesting, and I am surprised this type of paint is used, because I understood that it was based on metal compounds - but I am not sure - and particularly not sure if these are salts which perhaps do not have much conductivity - its one of the billion things I am curious about, but not curious enough to place investigation far enough up my list that I will look into it in this lifetime ;-)

Oh, just a completely OT aside..

I had an accident with a bottle of cynoacrilate adhesive (super glue) a couple of days ago - spilt a big blob onto my desk - I grabbed some kitchen towel to mop it up, but a few seconds after the paper touched the glue it burst into flames! Fortunately I have a piece of plywood on my desk when I do dirty jobs, so was able to lift the whole lot and take it outside and douse it in water...

Ever heard of anything like that before? - I wonder if it was some additive to the paper towel..

Those pens that you mention will almost probably be a mixture of azo (aniline based) dyes which are alcohol soluable. So for example, an orange pen would be a mixture of red and yellow, a purple pen would be a mix of red and blue and the black would maybe be a mixture of red and blue and orange and green and and and, all to make what is perceived as black.

I used to be into B&W photography and from time to time used to touch up small hair or dust specs which appeared as white on the final print-you have no idea how many different types of black there is!

In ye days of old, there used to marker pens which were non water soluble and used to contain azo dyes which were soluble in solvents such as benzene and toluene but those dangerous days are long gone now and so the dyes we are left with are different and to some extent less visually complex since they have to be alcohol soluble. Never-the-less, they mix well so complicated colour mixes can be produced.

As far as I know, there isn’t a simple spot test for carbon but then again, it’s a big world out there!

As far as your Super glue goes:

The initiation of the bonding in super glue is caused by moisture which causes a rapid polymerisation of the cyanoacrylate. This polymerisation is very exothermic (gives of heat).
In your case what probably happened was that since it was a big blob of glue contacting a large surface area of light fine paper (what kitchen towel really is) the glue generated enough heat to set the paper alight and since it was a big blob, would have kept on giving and giving-àfire.

Probably, if it had been a wee dab of glue, the paper would have been ok.

A similar thing can happen when using linseed oil with dry rags although it’s more of a slow burner :-)

Exothermic setting glues have been a bit of a problem for a long time: 30 years ago one of the main problems in hip replacements was keeping the glue from heating up too much too quickly which caused, among other things, much shock to the surrounding area.

(All reactions are either exothermic (give out heat/energy) or endothermic (take in heat/energy).
Generally reactions are more exothermic than endothermic since this means that the products have a lower energy than the starting materials and in nature, this is the general direction of travel.)

Oh Oh Oh Oh...

Think I might have found it!

Aniline Black ( http://www.kremer-pigmente.com/en/new-products/aniline-black-24100.html )

a.k.a.

Designers Gouache-Jet Black (http://www.winsornewton.com/products.aspx?PageID=164&ProductID=1400 )


Only potential problem is that according to my calculations it contains 16% Chromium w/w so not sure if this would pose a major problem.

Then again, as Fred suggested above, the fluorescent paint probably has a fair amount of metals in it and seems to be ok.

Stay tuned.