Borax Overglaze
Sundog
shows it, another I have does not....weird. Again I suspect Melissa ate it,
so anyway I repost for my and the public interest , and apologize for the
possible double post....but heh! )
Ok........ NOW this thread has my attention. Gil, I know you know about this
stuff, certainly more than most. Can you tell me then , what is going on
with the commercial products I have used for years for this:
1) Hotline Spray 'A' > I prefer this for the low fire temp, and lead
content is
no concern in my work really.
2) FuseMaster Super Spray > Low lead, but needs to fire higher, which
is not desirable at times
Do these use Borax as an ingredient too. Is there reason to worry regarding
durability on outdoor pieces with either of these clear glazes? I am far
more concerned
with quality and durability than with saving a couple of bucks short term.
Any specific suggestions?
While I am at it, what about Reusche low fire clear flux D2879, which I have
used indoors
as well? Everything seems to work well so far, but the concerns raised in
the original thread have me wondering about all this.
TIA, regards, Jacques Bordeleau.............. still buried in snow, in
Idaho
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O Pato
firing in the interest of eliminating surface crystallization -- also
referred to as devitrification. The tendency of any glass to crystallize
depends on its composition and the time/temperature treatment it is
given. Some glasses, like float glass or certain opal glasses readily
devitrify when exposed to a "fusing" firing as the readers here might
imagine. The overglaze on the surface of the article is a softer glass by
nature. That is, for a given temperature the overglaze will be less
viscous (more fluid) than the glass hosting it. The precise mechanism by
which overglazes work is unclear, but we could speculate that the
overglaze presents an environment in which anything that might
crystallize out of the host glass is amply soluble.
Using Borax to avoid Devit was originated by Ray Ahlgren. He found that
this worked particularly well with Spectrum's glasses, but with the
others, too. Spectrum published a pamphlet featuring Ray's technique,
which involves spraying a hot saturated solution of borax onto the work
prior to firing. Borax will melt to glass by itself at modest
temperatures and fuses before the host glass to resist crystallization.
It's a bit of a pain in the ass as a method, but has been shown to be
wholly successful in many applications. We should note that with the
Borax method there are no heavy metal issues for the tableware people.
>Do these use Borax as an ingredient too. Is there reason to worry regarding durability on outdoor pieces with >either of these clear
glazes? I am far more concerned with quality and durability than with
saving a couple >of bucks short term.
All frits (powdered glasses) which you might use to avoid surface
devitrification probably contained borax in the batch from which they
were made. All frits used in fusing overglazes are based on soft
borosilicate glasses, and borax serves to introduce the "boro" part, if
you will. One isn't aware that any fritmaker in the US is melting for the
sole purpose of making overglaze for fused glass. Seems like a year's
consumption for these ends would be a few hours production. Rather,
ceramic overglaze frits have been adapted to fused glass.
Commercial frits are compounded by highly competent individuals with high
chemical durability in mind. Nothing like having your frit dissolve away
in use to lose good customers, you know.
Spray "A" is (was?) Drakenfeld 61500 clear overglaze. The 615xx series of
ceramic overglazes were staple production for Drakenfeld for many years.
Of course, Drakenfeld has been through a number of changes in the past 20
years or so and the firm, now merged with Degussa, is now known as
Cerdec. In this the nature of the offerings have changed and it is
possible that the basic clear overglaze frit used for a Spray "A" sort
of product has changed, too. Probably to a version using less PbO and
more ZnO -- this would probably describe the harder of the overglazes
mentioned in a prior post. Enamels based on these and similar series of
ceramic overglaze produced by a variety of makers are all applicable to
all manner of baked glass processes.
The harder (higher firing) overglaze might reasonably be expected to
provide the highest durability -- this is a general rule, with notable
exceptions, of course. Choose an overglaze that will be sufficiently
fluid at the peak temperature required for the effects you want and the
glasses you use. What matters is that the overglaze fuses well onto the
surface of the ware. Underfired overglaze, if it contains PbO, may leach
Pb in amounts exceeding a variety of Standards of concern to people
making tableware. It is also possible that underfired overglaze will be
more susceptible to atmospheric attack than a well melted film -- there
are a couple reasons for this I'm not interested in going into right now.
It's late.
In fact, very little is known about the absolute durability of fused
glass surfaces produced by overglazing. One has seen several examples of
corroded overglazed fused glass outdoors, but really very few and most
showing poor technique in making or installation.
Really, it would be better if the glassmakers simply made glasses that
don't devitrify so easily. It's not that hard to do.
O Pato na beira da Praia
--
"It's not what we don't know that hurts, it's what we know that isn't so.
Barbara Cashman
with excellent results. For 1 gallon, (you could also halve the recipe), mix:
1 cup 20 Mule Team Borax
1 gallon of distilled water
mix well and crush out the lumps and let the sediment settle,
then cant
Add 1-11/4 c Klyr-Fire (from Thompson Enamel)--I understand
glycerine and gingerale would work here, but why bother. This mixture is clear,
and I use a foam painter's brush to liberally apply. Do not mix the solution
because it will eventually start to crystallize and settle in the bottom. And
remember to wash out the "brush" with distilled water, since the residue will
crystallize on it. I also use this coating when I am "glueing" pieces together,
since the peices will stick together when dried. It burns off beautifully, and I
didn't have to fire up a compressor. I fuse a lot of Spectrum, plus float.
Works great! If you have any questions, please let me know. Hope this helps.
Barbara
Sundog wrote:
> O Pato............. thanks, sir, for the info. Your moderately in-depth
> review of devitrification and overglaze was most welcome. Even with many
> years of fusing, I am not much of a chemist. I had some understanding of
> the issue, and now I have more. I will save it for tech referance.
>
> Well then I guess I am OK, using mostly Bullseye, which I find I often
> don't even need to glaze. I always glaze float glass of course, but only
> just enough to do the job, since I have suffered an undesireable milky
> effect when using too much. I apply it with an airbrush, and keep it as even
> as I can, applying several light coats to avoid the beading up effect of too
> much at once. And I always glaze Spectrum, which I fire as low as possible
> only for bending in lamp applications, since it seems to devitrify just by
> thinking about firing it. And I attempt to match the glaze to the working
> temps too.
>
> regards, Jacques Bordeleau
bert weiss
Thanks for your technique. I just emptied a kiln load that I applied
borax to with a mouth atomizer. I applied this from in front of the
glass, getting borax on one edge and the top of the glass. When I
opened the kiln each and every piece of glass had one white line of
stuck kiln wash where the glass spread from the heat . The borax
contacted the kiln wash and stuck. I think applying it with a hand
brush would eliminate that problem. Have you ever seen your overglaze deteriorate?
Bert
Bert Weiss Glass Studio
Painted Art Glass
Custom Productions
Architectural and Sculptural Cast Glass
Collaborative Art Glass
Lighting design
--
Barbara Cashman
brush, I let it dry first before putting in the kiln, since fingers have a tendency to
remove wet overglaze. Deteriorate? Am not sure what you mean. I only have
devitrification if I don't apply enough, or the solution has started to crystallize.
This formula makes a bunch, for pennies, so if it starts to crystallize, I just throw
it out. Barbara
Glas Wiz
Sundog,
Ok........ NOW this thread has my attention. Gil, I know you know about this
stuff, certainly more than most. Can you tell me then , what is going on
with the commercial products I have used for years for this:
1) Hotline Spray 'A' > I prefer this for the low fire temp, and lead
content is
no concern in my work really. ...... The real danger with all of the lead based
overglazes is to the person allying the spray. In the unfired state this stuff
can be pretty nasty... do not inhale.
2) FuseMaster Super Spray > Low lead, but needs to fire higher, which
is not desirable at times
Do these use Borax as an ingredient too. Is there reason to worry regarding
durability on outdoor pieces with either of these clear glazes? ... I can't
comment on what's in Spray A but I know that borax is not a component of Super
Spray. .....
I am far more concerned with quality and durability than with saving a couple
of bucks short term.
Any specific suggestions?
While I am at it, what about Reusche low fire clear flux D2879, which I have
used indoors
as well? Everything seems to work well so far, but the concerns raised in
the original thread have me wondering about all this.... I don't use flux
D2879, sorry... Gil
TIA, regards, Jacques Bordeleau.............. still buried in snow, in
Idaho
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Gil Reynolds gla...@AOL.com
www.teleport.com/~glaswiz/
15500 NE Kincaid RD. Newberg, OR 97132
T- 503.538.5281 F-503.538.6527
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Bob E Duchesneau
I never apply any anti divit spray when the object to be coated is on
the kiln shelf. Always spray outside of the kiln and then place the
object, which may still be wet, on the shelf. A good surface coating
seems to take care of the edges, perhaps, by spreading. Anyway I never
take any care to coat the edges and have had no problem.
Think the problem that you had was the borax formed its own glass from
what was over sprayed on the kiln shelf. B
--
Bob Duchesneau, Mountain Meadow Stained Glass 92026
Barbara Cashman
amount shoud be 1 to 1 1/4 cup. I'm sure you all understood, but wanted to correct
it.
Any other questions, please let me know. Barbara
Barbara Cashman wrote:
Bob E Duchesneau
pieces in the kiln
so that it can reach temp faster, and cool faster. This glass doesn't
usually devit.<<
I did not realize that you were using 1/2" glass that would tend to
spread at high heat.
I have had good luck with soaking glass at 1050'F for the few minutes
necessary to heat it uniformly through and then advancing at a high
rate (600 - 1000'F per hour) until the glass is formed. The high rate
of advance should reduce spreading and devitrification. I think it is
better to go higher than to hold at high heat to accomplish work. Also
the kiln will naturally come off high heat rather quickly. Bob
bert weiss
I did apply the overglaze off of the kiln shelf. I applied it with a
mouth atomizer, which got it on the top and the front edge of a piece of
1/2" float glass, which was fired to 1500F. at this temp the glass
spreads a bit on the shelf. Where the edge was sprayed with borax it
contacted the shelf after it spread, and left a white line of kiln wash
that won't clean off, only on one side. I'm pretty sure I could solve
this problem by applying the borax with a brush and not getting it on
the edge. The other solution is not to load so many pieces in the kiln
so that it can reach temp faster, and cool faster. This glass doesn't
usually devit. I was getting greedy and trying to make as many pieces
as fit in the kiln. When I use 1/4" float it usually does devit, unless
covered with borax, or some other overglaze. Fortunately borax does not
seem to react with the tin side of float glass.
Bert
Bert Weiss Glass Studio
Painted Art Glass
Custom Productions
Architectural and Sculptural Cast Glass
Collaborative Art Glass
Lighting design
Bob E Duchesneau wrote:
>
> Bert,
> I never apply any anti divit spray when the object to be coated is on
> the kiln shelf. Always spray outside of the kiln and then place the
> object, which may still be wet, on the shelf. A good surface coating
> seems to take care of the edges, perhaps, by spreading. Anyway I never
> take any care to coat the edges and have had no problem.
>
> Think the problem that you had was the borax formed its own glass from
> what was over sprayed on the kiln shelf. B