So yeah. I once got a glimpse on some picture in the gallery a few years ago, that an arc tube of a HPS lamp is great at knife sharpening. Yeah, it is. Recently I ordered two 600 watt HPS lamps for my collection, and one came smashed open because the seller was a nutjob and packed it up like it was metal spoons inside. So I smashed away the remaining glass and cut out the arc tube and tried to sharpened my kitchen knifes just for the hell of it. Oh. My. God.  It sharpened my knifes in only a few passes to an extent that one of my dullest knifes diced a mushy old tomato without any mess at all. It cut the skin like it was NOTHING!  Guys! Get yourself a HPS lamp, smash it open, take out the arc tube and use it to sharpen your knifes! It works amazingly and much better than any of the stone sharpeners I ever used in my entire life!

Anyway, I just wanted to share my experience 

I see as a not that bright idea to mess up with those lamp internals around something that is then used for handling food. There too nasty things used in lamps: Mercury, baryum,... Not something I would like to have in my meal...

Buy a wire brush or a grinding stone to sharp your knifes.

The only thing I can imagine a HPS arc tube being poisonous to humans is if the arc tube is pulverized and then inhaled as dust. It is toxic if inhaled. Since the arc tube is fused in a kiln, it is stronger than glass, its more like a gem stone of sorts in terms of hardness, and the fact that it removes the metal from high grade stainless steel knife shows that the arc tube material is much stronger than steel and therefore it is not dangerous in any way. Plus I always wash the knife after sharpening so all the minute shavings of steel get washed away. So if you know a thing or two about lamps, using a HPS arctube t sharpen the knife is really not dangerous at all and does not pose any risks 

You'll never sharpen a knife with a wire brush... 

What we use is a Chef's Steel similar to this one, and it keeps our set of knives, which I've had for over twenty years, razor sharp. 

I use back of ceramic bowl to sharpen  razor blades for wire stripping and kitchen knives too.

You'll never sharpen a knife with a wire brush... 

What we use is a Chef's Steel similar to this one, and it keeps our set of knives, which I've had for over twenty years, razor sharp. 

When the storage of Carmel hospital, had a bench grinder with a wire brush to grind duplicated keys, I managed to sharp scissors using the bench grinder wire brush, by cleaning it from dirty.

@ Dor, you might have been able to clean the scissors, but there's no way that a wire brush, even if it's attached to a bench grinder can put a sharp edge on a blade that is considerably harder than it is.

This topic seems at risk of going south.

Its a cool discovery that HPS tubes can sharpen knives, but its important to remember that the best way to sharpen knives is with the proper equipment. Especially for one's in contact with food.

Strangest thing I’ve ever used a HPS tube for was as a heater support in my old tumble dryer!
The original support on one of the heater coils was a long piece of mica which snapped in the middle causing the top coil to bend and short out on the middle coil!, as I didn’t have any mica long enough, I threaded an EOL HPS tube in between the top coil to keep it straight!, worked for a few more years after that! 

That is the most clever solution i have ever seen to a problem i might face myself someday!!  thank you for sharing! 

If one sharpens on a standby lamp, would it sharpen twice as fast?

The Alumina arc tube of HPS lamps is a remarkable material, and indeed incredibly hard.  In the lamp factories they are well known for sharpening blades far more effectively than many commercial devices - and are also widely used as glass cutters.  Most glass cutters have carbide steel blades but those quickly become blunt since glass is a harder material.  They could be sharpened again with an HPS arc tube - but far more effective is to just use the sharp squarely-cut end of the arc tube to scratch the glass.  They last for years without wearing.

It is true that if one should break open it may release mercury - but they are so hard and impact resistant that even an arc tube thrown with some force onto a concrete floor will rarely break.  The alumina itself is almost completely inert and safe amongst food products.  In fact many of us are in regular contact with alumina - modern dentures were created as a direct spinoff from the materials technology of the lamp industry and use the exact same material - although not sintered to quite the same degree so as to avoid them becoming too translucent.

Another material that made its way into everyday life for thousands of lampmakers is the Tungsten Brillo Pad.  Brillo pads are maybe not known by that brand name in all countries - they are small abrasive steel wool pads used for scouring and cleaning in the kitchen.  The steel wires are typically drawn with a triangular cross-section to make them more abrasive.  But steel is a soft metal which quickly wears out, and it corrodes in the presence of air and water.  The pads are always disintegrating into a rusty old mess.  Some modern equivalents are made of non-corroding alloys but still far too soft and regularly wearing out.  Tungsten meanwhile is both inert to household products and considerably harder - but lamp wire is perfectly smooth and not very abrasive.  However, lamp filaments are made from coiled and coiled-coiled wires, and the multiple surfaces makes them superbly abrasive.  There tends to be rather a lot of scrap from the coilwinding process, filaments whose coil pitch varies by as little as a millionth of an inch are scrapped because lamp life may be negatively impaired.  The waste is of course normally returned to the tungsten wire plants for recycling.  But not before factory employees have taken home a handful to begin a lifetime’s work in the kitchen!  Filaments of each design have carefully chosen wire and pitch ratios to avoid them becoming interlocked and sticking to each other.  But the scrap bins contain a mix of everything and all those different coils become a tangled mess that is locked together for life.  Two of my grandparents worked in an electronic tube factory which had a similar demand for the tungsten heater coils of the cathodes.  Long before I knew much about lamps I remember doing their washing up with the tungsten scouring pads they’d been using since the 1950s, almost undiminished from their original proportions.  And then made my own when starting work at a lamp plant - which is still perfectly intact some 25 years later 🙂

The thing I would be worried about is not the alumina (or tungsten) to be dangerous by themself, but unlike the clean materials smuggled from the lamp factory before they came in contact with anything nasty, the pieces taken from an already complete (and more over worn out) lamp means all of those are more or less contaminated by the stuff used in the lamp, mainly the Hg and Ba. And I just wouldn't trust they won't get released (alumina itself is inert, but the amalgam smeared on its inner surface when operating 20+khours as a HPS lamp isn't inert at all)