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  1. #1
    I've searched all over the internet to see what causes that white crystal powder on fireplace glass. My guess is it's the mineral deposits left over as natural gas burns;or is it the sulphur and butane and other chemicals left over after natural gas is burned. Is it the thermal decomposition of Mercaptan after natural gas is burned? What about hydrogen sulfide and oxides of sulfur, carbon?
    This fire place glass was covered by this stuff, how do I fix it. Told customer to call original installer to fix problem. Glad I didn't have to deal with it.

  2. #2
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    I have heard it is the mercaptan, but personally it seems to me it is mostly cause by the burn off of DUST. I mostly see the white film on B-Vent units, which take room air for combustion. Seems that in more dusty conditions there is more white crud on the glass.

    Best ways to get it off is using a product called "White Out" (no, not the liquid paper stuff) or something similar. Should be available at a hearth store.

    Also using a VERY sharp scraper blade with the white out product or some Windex w/ vinegar works when its really stuck on.

  3. #3
    Join Date
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    incomplete combustion at the pilot combined with high humidity. Same thing happens in furnaces. No ammonia based cleaners on the glass/ceramic. If it is bad enough, it will etch the glass.
    I love my job, but paydays Thursday

  4. #4
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    Exclamation cleaning tempered glass

    It isn't recommended using sharp objects around tempered glass. Could nick the glass causing a stress point that could lead to shattering.

    No ammonia-based cleaners. You can use White Off, which works great, which has been tested by Schott Glass Co.. You can also use Brasso or Noxon metal polish. These were tested by Heatilator and acutally mentioned in their manuals. You can also use any of those creamy cleaners for ceramic glass cook tops such as Ceramabryte.

    As for the chemical analysis of the white residue, it is a combination of minerals and acids. Understand the amount of sulfur in NG and LP from both hydrogen sulfide and mercaptans is in the range of parts per billion.


    The key to this white residue is time. The longer it stays on the less you will be able to get off even with White Off or other polishes, which are really just microabrasives. You get crazing of the glass, which is permanent damage. On new Fps, clean the glass after the first few hrs. then as needed but at least several times a yr. Always inspect the gaskets for good contact and don't burn Fps with the glass clips loose or the glass off on units designed to burn with the glass sealed.

    Glass facts: soda-lime tempered glass is rated 550F. borosilicate glass about 800F while ceramic glass is 1,400F

    Ceramic glass can take thermal shock while tempered glass cannot.

    When cleaning tempered glass, remove all diamond rings and never lean the glass agains the corner of a raised brick hearth or similar hard point. Don't let kids and dogs walk on the glass while cleaning. Neither belongs in the room when servicing a Fp.

    Never throw champagne glasses into a factory built Fp.
    Never try to clean glass while hot. Allow it to cool entirely. Tempered glass hit with cleaner will lose its temper in that one point setting up stress lines that will result in shattering.

  5. #5
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    Apr 2002
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    There is a small amount of sulphur in natural gas. When the gas burns, it produces sulphuric acid, which (along with the water vapor produced when gas burns) condenses on the glass.

    Hot sulphuric acid vapor is also held against the glass when the burner is operating.

    The hot acid etches the glass, and the whitish powwder is your glass. When the glass is new, this powder can be cleaned off easily, but when the glass gets etched deeply enough, nothing will clean it off, and you need to order new glass from the manufacturer if you are unhappy with what you can see.



    Seattle Pioneer

  6. #6
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    sulfur in NG?

    I get this business of sulfur in NG & LP all the time. The fact is, the utilities keep it under the 0.3 grains of hydrogen sulfide per 100 cubic feet as prescribed by the gas codes. They don't like to comply but they do for liability reasons. I've had the gas tested by a lab. The Ph.D. assures me you are looking at parts per Billion of sulfur, which is nowhere near enough to form any appreciable quantities of H2SO4. There are many other acids that form including HCL and nitric acid for starters.

    There USED to be a lot of sulfur in the gas back in the 60's and before. However, once the sulfur was proven the culprit in enough Oops!s, they put the restriction in the gas code. While the gas codes don't regulate the refineries, it puts pressure on them to comply or else they would be negligent. There was a bit of litigation surrounding copper sulfide production, which tends to clog valves and valve seats. This is why many valves have inlet screens. It is also why they want sediment traps installed (along with a lot of other crap in the lines).

    Now, having said all that, you just wait for this winter when they start spiking the gas with anything they can get their hands on from propane to butane to CNG.

  7. #7
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    Well, Hearthman ---

    This is the explanation I was given by engineers at the gas utility where I worked. They could be wrong, I suppose.

    My own observation is that the white powder does appear to be glass that is etched off by something. This also explains why fireplace glass can be cleaned for a while, but eventually becomes permanently clouded ---that's when the glass is etched deeply enough to permanently damage the glass.

    Do you agree with me that the whitish powder is glass that has been etched? If so, what is the agent that is causing that detrioration, if not the sulphur?

    Personally, I trust the gas utility engineer over your PhD in a testing lab who might not be deeply involved in the problems of natural gas combustion. And I seem to recall that there is a good deal more sulphur in natural gas than would be commonly measured by a few parts per million, but that memory is vague.

    I'm not necessarily claiming that my theory is right and yours is wrong, although so far I still find my theory more convincing.



    Seattle Pioneer


  8. #8
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    white stuff

    S/P. no slight to you intended-- just another point of view.

    Yes, the glass does get etched but keep in mind there are several acids being formed in there including hydrochloric and nitric acids.

    I dunno who is right but Dr. Streit has won for us everytime she's gone to bat for us and is recognized as an industry expert in surface analysis. She has measured the levels in sulfur on the glass using Scanning Electron Microscopy long with X-ray Fluoroscopy and, again found only trace evidence. This is like spreading one fraction of a single grain of salt throughout this volume.

    If someone can do the calculations, figure 0.3 grains of HSO per 100 cubic feet.

  9. #9
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    Moose Jaw, Saskatchewan, Canada Occupation:Interprovincial Plumber, Commercial Gasfitter Interests:
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    Up here, we have very clean gas. I went to look at a furnace in a house that was for sale. Right next to the furnace was a crawl space with extremly high humidity. All that was running on the furnace was a HUGE pilot flame. The cell above the pilot was plugged with white powder. Just for giggles, I fired the furnace and the flames rolled out the front. Next time you see white glass, note the humidity and see if it is high.
    Some of the guys from Napoleon felt that high humidity is the major factor.
    I love my job, but paydays Thursday

  10. #10
    Join Date
    Apr 2002
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    Hello Rich P,


    The white powder that tends to accumulate on a furnace over time is usually zinc oxide from the zinc on galvanized vent pipe or other galvanized parts. The zinc is there to protect the underlying steel from rusting, but over time the zinc corrodes into zinc oxide, the same stuff mountain climbers put on their nose to prevent sunburn.

    That's different from the white powder on fireplace glass.

    Or that's my story, anyway. Someone may want to dispute my zinc oxide theory!



    Seattle Pioneer

  11. #11
    Join Date
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    Moose Jaw, Saskatchewan, Canada Occupation:Interprovincial Plumber, Commercial Gasfitter Interests:
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    This is different. it is inside the hx and is soft and powdery.
    The stuff in vents is usually hard.
    I love my job, but paydays Thursday

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