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Author Topic: [Q] On the Working of Slate  (Read 1961 times)
von Corax
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Prof. Darwin Prætorius von Corax


« on: June 25, 2012, 10:20:11 am »

I've recently learned that I might have an opportunity in the not-infinitely-distant future to acquire one or more used slate roof tiles; such big slabs o' rock might be ideal for the replicating of the gorgeous slate-backed electrical switch panels which appear in photographs in these fora from time to time.

My question, then, is whether any of you kind gentlefolk have experience you are willing to share in the safe drilling, milling or machining of slate?

My gratitude in advance,

Prof. Darwin Prætorius von Corax, Lead Systems Engineer
The Leverkusen Institute of Paleocybernetics
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« Reply #1 on: June 26, 2012, 12:12:54 am »

I've cut slate with an electric tile saw. The diamond wheel type.

The wheel runs in a water bath to cool the operation and flush the fine slate dust from the wheel.

Don't do anything that involves cutting the stuff dry. The dust is very bad for you. In the area of North Wales around Ffestiniog where the slate was mined, the chapel yards are full of gravestones made out of the same stuff that killed the person beneath.

Maybe look at Lapidary suppliers for suitable polishing compounds.
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von Corax
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« Reply #2 on: June 26, 2012, 09:38:59 am »

A tile saw. Thank you, Dr. Q, that would not have occurred to me (although I suspect it should have.) I last worked stone in summer camp, several decades ago.

So for drilling, would one use a technique similar to that used for glass ie. diamond drill surrounded by a plasticene dam filled with water?
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« Reply #3 on: June 26, 2012, 06:22:15 pm »

If we are talking REAL slate, then for drilling all you need is a firm board to lay the slate upon (it is weak and won't deal well with flexing...), and apply gentle pressure using a standard electric drill fitted with a normal masonry drill bit. For larger holes, a hole saw works just fine.

To be honest, it's soft enough that you can cut and score it with a sharp work knife.

Be *sure* that it is genuine slate and not a later manmade product - this is nearly always made with ASBESTOS!  If you see a fibre like material where the surface has worn with age, don't touch it and leave well alone.

I'm from a long line of builders, and I've plenty experience with roofing slate. Wink



However, you may have some issues trying to smooth and polish slate, it doesn't really lend it's self to that. You will have to use a special compound applied in numerous layers to build up a shiny surface. It's not too likely to be 'mirror like' either... A cheaper alternative is to build up successive layers of black boot polish, using a heat gun to melt it into the surface. Then apply a layer of wax, such as beeswax, and buff to a shine. Do it outside though, the fumes are strong! Wink

I think most people are confused by the use of the name "slate" - Slate used for roofing is a soft easily split stone, whereas the "slate" described in antique switchboards etc typically isn't SLATE - it seems to be a number of different items, including some that were manmade!  People tend to call any polished black material "slate", as it's a common term. But it's incorrect.

In MOST cases, "slate" used to describe the polished black material used for antique fire surrounds and antique Victorian clocks and other decorative items, is actually a type of MARBLE - carbonaceous limestone to be exact. I believe it typically comes from an area in France.


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von Corax
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Prof. Darwin Prætorius von Corax


« Reply #4 on: June 29, 2012, 06:06:17 am »

Be *sure* that it is genuine slate and not a later manmade product - this is nearly always made with ASBESTOS!  If you see a fibre like material where the surface has worn with age, don't touch it and leave well alone.

I'm from a long line of builders, and I've plenty experience with roofing slate. Wink
It's a church roof which (if I recall correctly) was replaced within the past few decades, so if it's synthetic it's unlikely to contain asbestos, although I'm sure the financial records still exist if I need to consult them.

I think most people are confused by the use of the name "slate" - Slate used for roofing is a soft easily split stone, whereas the "slate" described in antique switchboards etc typically isn't SLATE - it seems to be a number of different items, including some that were manmade!  People tend to call any polished black material "slate", as it's a common term. But it's incorrect.

In MOST cases, "slate" used to describe the polished black material used for antique fire surrounds and antique Victorian clocks and other decorative items, is actually a type of MARBLE - carbonaceous limestone to be exact. I believe it typically comes from an area in France.
That could explain a few things. The first time I saw such a switch panel (and I desperately wish I could find the photos — it was utterly gorgeous!) I described it as marble (or possibly granite), but someone corrected me and said it was slate. Oh, well.

Can anyone tell me if real slate has the structural integrity to back a mains switch?

(Hmm… black granite countertop offcuts… We really need a "deep in thought" smiley!)
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« Reply #5 on: July 08, 2012, 07:29:07 pm »


Can anyone tell me if real slate has the structural integrity to back a mains switch?

Yes, it does, but finding switchboard-quality slate panels may be tough. Here's what the good stuff looks like.

That's a generator control panel from a dam in Washington State, and that was a live panel when the picture was taken in 1995. The polished slate panels are an inch thick. 

You can get slate countertop material. That has a polished surface and is about an inch thick. It might be easier, and lighter, to get slate floor tiles, which are much thinner. They'll need to be backed with something for structural strength.

Some slate has metallic incursions, often copper. These show as veins in the rock, and are conductive, so you don't use those in live-front switchboards.
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von Corax
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Prof. Darwin Prætorius von Corax


« Reply #6 on: July 09, 2012, 04:41:49 am »


Can anyone tell me if real slate has the structural integrity to back a mains switch?

Yes, it does, but finding switchboard-quality slate panels may be tough. Here's what the good stuff looks like.

That's a generator control panel from a dam in Washington State, and that was a live panel when the picture was taken in 1995. The polished slate panels are an inch thick. 

You can get slate countertop material. That has a polished surface and is about an inch thick. It might be easier, and lighter, to get slate floor tiles, which are much thinner. They'll need to be backed with something for structural strength.

Some slate has metallic incursions, often copper. These show as veins in the rock, and are conductive, so you don't use those in live-front switchboards.


All good to know, but the slate I expect to have access to is from the roof of a local church which is being deconsecrated and demolished. (All of the furnishings are looking for good homes — I have already called dibs on a lectern which was donated by one of my ancestors.) I expect the salvagers will sell off most of the slates, but I figure I could lay claim to a handful of them.
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Wilhelm Smydle
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« Reply #7 on: October 25, 2012, 09:49:32 pm »

Slate actually works well for pierce work though it can still be fragile.
I have seen a few projects where the slate tile was backed with oak to give above contrast.
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