Karl Platt on tue 17 sep 02
The basic of the initial inquiry:
DSN> Is there anyone out there who has tried to melt a large amount of glass in a
DSN> bowl? Not just incorporating a few pieces here and there, or one piece down
DSN> at the bottom of something....but a significant amount, of around 1 inch or
DSN> more deep.
Sure. In fact, if you go the the Herald Square subway station in Manhattan, where you'd get off to go to Macy's, and notice the CdSSe orange warning strip in the
platform, you'll see that it's glass fused onto ceramic -- and that it's not crazed or notably worn after 10 years of service. While the glaze/glass film is not 1" thick -- it's
something more like 1/4" -- the same rules would apply to making an object like that described above. No, I'm not going to give anyone a "recipe" to pull it off, but I
will give some useful hints.
The thermal expansion issue was raised in earlier responses. The long and short of it is that most clayware bodies used for studio work -- stoneware, porcelain, etc.--
have expansions vastly different from those of most glasses you'd encounter.
Bullseye's glass was mentioned in one reply. The nominal expansion of their glasses has been said to be on the order of 90 x 10^-7, and they are also quick to note
that expansion is not necessarily the sole factor in determining whether things fused of glass will remain whole. Things like temperature/viscosity relations between the
different glasses also have serious consequences. This was noticed early on by lensmakers who wanted to make bi-focals by fusing different glasses together.
There's an Article in a 1930's Glass Technology describing these complications. The vacuum tube makers also confronted this behavior between the soda glass
used for the envelopes and the lead glasses used to seal the wiring into the tube. Several articles in the literature address this issue also. Temperature/viscosity
differences was again observed as a complication and then studied by vitreous enamels people (Drakenfeld -- remember them?) whose customers were having
quality problems, i.e. flaking decoration on bottles. There's a brief article in an ACerS Journal from the 50's (I think) that describes this behavior and its practical
resolutions in a little detail. Perhaps someone from the Society would be kind to look this up for us.
Similar behavior is also seen amongst various ceramic glazes on clayware where two glazes that fit fine on a given substrate (body) individually will crack or spall off of
each other.
That out of the way we get to the fact that most clayware has expansions on the order of 65-70 x 10^-7/ºF, which makes it unsuitable for use as a substrate for most
colored glasses you'd find -- like Bullseye's. As such one is obliged to seek out either lower expansion glasses and/or higher expansion ceramics if they want them to
mate.
High soda spar and replacing Sand with alumina in porcelain type bodies is one approach to making high expansion bodies -- these also evade to a good extent
"fitting" issues related to the changes silica undergoes at 573 ºC. MgO bodies like steatites are also useful in this application -- these are widely used for electrical
insulators where alkalies are to be avoided. Such bodies aren't horribly dissimilar from the talc/ball clay versions used for silp cast hobbyware. This is to say that if you
want to find high expansion body "recipies" there are plenty published.
If one wants to take the lazy man's approach to putting glass on clay and not make their own, it's best to select glass used for ovenware, which has expansions more
nearly approaching those of more common clayware bodies. A lot of this glass is 50-60 expansion and there are a few colors available -- amber, Ni-Co bluegreys, and
that great purplish stuff.
OK, I'm off to bed.
Best wishes for success
P.S. The reason SnO(2) is given a low "factor" in expansion calculation schemes, which are not too far removed from throwing darts blindfolded if you depart from the
range of composition for which they were developed, is that it can replace SiO2 in the glassy network, strengthening it relative to other components which disrupt the
network, thus having the net effect of lowering expansion. E&T numbers are completely useless for glazemaking, and are of limited use to glassmakers. Appen was
an enamel maker and his many years of study and analysis of these materials, which are much more nearly akin to ceramic glazes, make them a better choice. For
those who are literate in German, Appen's work is a great and very valuable read.
KPP -- Stirring the pot
Ditmar on wed 18 sep 02
Haven't seen the specific strips you're referring to.
Glass tiles and strips are quite common though. If properly set they may
give the idea that the glass is fused to a ceramic backing.
Ditmar
----- Original Message -----
From: "Karl Platt"
To:
Sent: Tuesday, September 17, 2002 5:41 PM
Subject: Glass Question Response
> The basic of the initial inquiry:
>
>
> Sure. In fact, if you go the the Herald Square subway station in
Manhattan, where you'd get off to go to Macy's, and notice the CdSSe orange
warning strip in the
> platform, you'll see that it's glass fused onto ceramic -- and that it's
not crazed or notably worn after 10 years of service. While the glaze/glass
film is not 1" thick -- it's
> something more like 1/4" -- the same rules would apply to making an object
like that described above. No, I'm not going to give anyone a "recipe" to
pull it off, but I
> will give some useful hints.
Dwiggins, Sandra (NCI) on wed 18 sep 02
Karl wrote:
... No, I'm not going to give anyone a "recipe" to
pull it off, but I
> will give some useful hints.....
Why don't you give the "recipe" to pull it off? It might be extremely
helpful if you actually have one.
Hints are fine, too, but why holdout if you have the answer? Not that I
didn't appreciate your hints...they were great, in fact I was hoping there
was a glass person tuning in to Clayart.
Sandy
> -----Original Message-----
> From: Ditmar [mailto:gaylecat@MAUI.NET]
> Sent: Wednesday, September 18, 2002 12:08 PM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: Glass Question Response
>
>
> Haven't seen the specific strips you're referring to.
> Glass tiles and strips are quite common though. If properly
> set they may
> give the idea that the glass is fused to a ceramic backing.
> Ditmar
> ----- Original Message -----
> From: "Karl Platt"
> To:
> Sent: Tuesday, September 17, 2002 5:41 PM
> Subject: Glass Question Response
>
>
> > The basic of the initial inquiry:
> >
> >
> > Sure. In fact, if you go the the Herald Square subway station in
> Manhattan, where you'd get off to go to Macy's, and notice
> the CdSSe orange
> warning strip in the
> > platform, you'll see that it's glass fused onto ceramic --
> and that it's
> not crazed or notably worn after 10 years of service. While
> the glaze/glass
> film is not 1" thick -- it's
> > something more like 1/4" -- the same rules would apply to
> making an object
> like that described above. No, I'm not going to give anyone a
> "recipe" to
> pull it off, but I
> > will give some useful hints.
>
> ______________________________________________________________
> ________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
Karl Platt on thu 19 sep 02
>Why don't you give the "recipe" to pull it off? It might be extremely
>helpful if you actually have one.
If I actually do?! Smartass.
This gets the Frederick Carder response:
"Why should I tell you in five minutes things that took me years to learn?"
I have no problem with assisting the curious interested in resolving their challenges, but no patience for sheer sloth, which is what you'd apparently have me indulge.
Well, that's not part of the local reality.
>Hints are fine, too, but why holdout if you have the answer? Not that I
>didn't appreciate your hints...they were great, in fact I was hoping there
>was a glass person tuning in to Clayart.
There are, alas, too many who appreciate what they pillage.
As a heads-up, I've been "tuning-in" to Clayart since Clayart was five of us and you were ahead to know Unix to post.
Since they let the barbarians in there's all too much selfish and braindead gimme gimme and and the tedious miasma of the same topics that were answered well
almost 10 years ago. If anyone would bother to look in the archives there's be a lot less Clayspam on this list, but that would take effort.
I'm outta here.
KPP-- @ nomail
John Britt on thu 19 sep 02
Well,
That sure was a shame to loose Karl Platt! It has been a pleasure to read
his posts.
A sad day,
John Britt
Ron Roy on sun 22 sep 02
Because - you might just need the same type of information yourself in the
future - for one thing. Because you are a human being and can for another.
RR
>"Why should I tell you in five minutes things that took me years to learn?"
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
| |
|
