C. A. Sanger on sat 1 feb 03
A colleague who likes to spray glazes is having problems with his glazes
forming a snow-powder-like coating that does not fire out smooth, but
stays textured. He has tried adding more water, and glycerin, to no
avail. Would a different sprayer help, maybe the new HVLP ones
mentioned here? Any suggestions? I am afraid I couldn't offer advice
as I dip or pour. Thanks! C. A. Sanger
ShardRock Clay Studio <:)}}}><
Herington, Kansas
Nanci Bishof on sat 1 feb 03
Don't know what the reason is for them staying dry matt grainy textured.
I've had the same thing happen when I sprayed a glaze I formulated as a ^04
even when fired to ^6 that when brushed on and fired to ^6 was a nice melted
crystal matt. I just decided I wouldn't spray that glaze. Any hypothesis
would be welcome.
nanci
george koller on sat 1 feb 03
Fast note to C A Sanger
I won't try and guess the problem further than to say that if the same
gun was working and stopped, and assuming the glaze formulation
is the same then what he may be experiencing could be related to dry
glaze build up in the mixing chamber. This will happen if you don't
get the gun completely clean after each application. I suspect that some
pretty expensive guns might be worse than the cheaper/simpler units
in this respect. Spraying water out after each application should help
avoiding this problem, but from where he is now will likely require
disassembly and brushing out.... the manufacturers make kits for this
and there are generic kits (a good opportunity to pay $8 for 3 toothpicks
and a small bottle brush).
Second, I would like to mention that the Harbor Freight HVLP spray
systems have a HUGE nozzle size of 0.70". I have to think that is an
advantage when dealing with glazes - but my own experience is limited
to a dozen or so spray sessions. The latest catalog shows the
44802-3MGA as being on sale again at $69.99 (which is as cheap as
I've seen these things).
A word of warning however, these guns "take some getting used to"
because air is coming out of them all the time. I found I had to get
farther from the work than I was used but that I liked the overall ability
to get more material to get the glaze applied quickly, but I spray
mostly downward on tiles laying flat.
My 2c worth, hope it might help.
George Koller
Sturgeon Bay, WI - Door County
"C. A. Sanger" wrote:
> A colleague who likes to spray glazes is having problems with his glazes
> forming a snow-powder-like coating that does not fire out smooth, but
> stays textured. He has tried adding more water, and glycerin, to no
> avail. Would a different sprayer help, maybe the new HVLP ones
> mentioned here? Any suggestions? I am afraid I couldn't offer advice
> as I dip or pour. Thanks! C. A. Sanger
>
> ShardRock Clay Studio <:)}}}><
> Herington, Kansas
>
> ______________________________________________________________________________
> 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.
Vince Pitelka on sat 1 feb 03
> A colleague who likes to spray glazes is having problems with his glazes
> forming a snow-powder-like coating that does not fire out smooth, but
> stays textured. He has tried adding more water, and glycerin, to no
> avail. Would a different sprayer help, maybe the new HVLP ones
> mentioned here? Any suggestions? I am afraid I couldn't offer advice
> as I dip or pour. Thanks! C. A. Sanger
C.A. -
This problem is almost always because the spray gun is held too far from the
work, and the spray dries before it hits the work. In that case, the fired
glaze never fluxes into a continuous coat, and often comes out like
sandpaper. The solution is to hold the spray nozzle closer to the work, so
that the spraygun creates a moving puddle of glaze on the surface. With a
little sensitivity, you can control this without the glaze running. It is
very important that you watch for and control this "wet spot" created as the
glaze hits the ware. If you don't see the wet spot, then the glaze is
drying before it hits the ware.
Good luck -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://iweb.tntech.edu/wpitelka/
Vicki Hardin on sun 2 feb 03
I've noticed with some glazes that spraying distance and the amount sprayed
makes a difference in whether or not the glaze goes on smooth. I have a
friend that uses this to make a crawler glaze give an orange peel effect.
The other thing that I can think of is that possibly the glaze is not staying
suspended and settles out in the canister? BTW, the best sprayer I have ever
seen is a gun that is used to wash auto parts. It has a hose that goes into
a glaze bucket and is hooked up to an air hose. To clean up, you put it in a
bucket of water, hold your finger over the nozzle and spray afterwards
letting the water run through the gun.
Vicki Hardin
http://vickihardin.com
http://ClayArtWebGuide.com
http://iloveclay.com
john forstall on sun 2 feb 03
C.A.Sanger,
Assuming the spray gun is working for most glazes, your friends spraying
problems sound related to the bisque rapidly sucking the water out of the
glaze leaving a powered surface instead of a smooth wet
one. Some glazes do this to a greater extent than others. The solution
I've found is to spray the piece with plain water before glazing. Some
experimentation will be needed to determine how wet to make the bisque
before the glaze runs or curtains when applied. For one of my troublesome
glazes I dip the smaller bisque pieces in a bucket of water before spraying
the
glaze. If the piece is too wet when spraying just set it aside for a couple
of hours and try again. This has been working for my for years.
John Forstall
In Pensacola FL.
Roger Graham on mon 3 feb 03
I've been following the posts re the sprayed-on glaze which when fired
didn't come out as smooth as expected. Not all of the answers so far have
appealed to me much. For what it's worth, here are two more ideas:
1. If the fired surface is dry and scratchy, when it was expected to be
shiny and smooth, it's likely that the sprayed coat was simply too thin.
It's not easy at first to estimate by eye when to stop spraying. For
reliable results every time, it pays to estimate the area of the surface to
be sprayed, and measure out the appropriate volume of glaze. By way of
example, my most-used temmoku glaze requires 10 millilitres by volume for
every 100 square centimetres of pot, to get a rich dark surface. A thinner
coat may look much the same before firing, but isn't the same at all when
fired.
2. If the fired surface is dimpled and bumpy like orange peel, instead of
glassy smooth, the likely cause is adjusting the spray gun to deliver coarse
drops rather than a fine spray. This effect shows up worst if the glaze is
not very fluid, so the surface doesn't even out when hot. By way of example,
the talc white glaze we use for the interior of domestic pots shows this
effect inside big mixing bowls. To get the desired smooth quality finish,
it's necessary to adjust the gun to deliver a mist of fine droplets. Doesn't
matter at all if the surface is powdery, so long as the sprayed coat looks
smooth. This one needs only 6 millilitres for every 100 square
centimetres... just measure the appropriate volume, and spray it on with the
gun adjusted correctly.
I don't find it necessary or desirable to aim for a wet fluid patch where
the spray lands on the pot. Better to back off a bit, adjust the width of
the spray pattern to match the pot, and adjust the air flow for a fine
spray. No need for excess air to cause unwanted overspray... if you set the
gun right, the glaze lands on the pot and stays there. Smooth is beautiful.
Roger Graham, near Gerringong, Australia
http://members.optusnet.com.au/~rogergraham
David Hewitt on mon 3 feb 03
Yes, I would agree that spraying distance and amount sprayed makes a
difference.
Too close and the spray can 'blast' off the glaze and look too liquid at
that point. Too distant and the glaze can look powdery. The amount of
water in the glaze mix can also be a factor.
I spray a lot of my work and I find that consistency in the above is
important to get consistent results.
I would never spray first with water, as has been suggested. This is not
only unnecessary in my view, but also adds another variable into the
equation. A soaked pot will take up less glaze than a dry pot.
David
In message , Vicki Hardin writes
>I've noticed with some glazes that spraying distance and the amount sprayed
>makes a difference in whether or not the glaze goes on smooth. I have a
>friend that uses this to make a crawler glaze give an orange peel effect.
>The other thing that I can think of is that possibly the glaze is not staying
>suspended and settles out in the canister? BTW, the best sprayer I have ever
>seen is a gun that is used to wash auto parts. It has a hose that goes into
>a glaze bucket and is hooked up to an air hose. To clean up, you put it in a
>bucket of water, hold your finger over the nozzle and spray afterwards
>letting the water run through the gun.
>
>Vicki Hardin
>http://vickihardin.com
>http://ClayArtWebGuide.com
>http://iloveclay.com
>
--
David Hewitt
David Hewitt Pottery
7 Fairfield Road, Caerleon, Newport,
South Wales, NP18 3DQ.
Tel:- +44 (0) 1633 420647
Fax:- +44 (0) 870 1617274
Web:- http://www.dhpot.demon.co.uk
Vince Pitelka on mon 3 feb 03
> I don't find it necessary or desirable to aim for a wet fluid patch where
> the spray lands on the pot. Better to back off a bit, adjust the width of
> the spray pattern to match the pot, and adjust the air flow for a fine
> spray. No need for excess air to cause unwanted overspray... if you set
the
> gun right, the glaze lands on the pot and stays there. Smooth is
beautiful.
Roger -
This may work for particular glazes you use or for a particular spray gun
you have, but otherwise it is questionable advice. The best way to get the
equivalent of a "flowing coat" (as one would get by dipping or pouring a
glaze) is to watch that wet area where the spray hits the pot. As I said in
an earlier post on this subject, if a glaze fuses easily, then it may not be
much of an issue whether or not the sprayed surface is granular or powdery.
But a more recalcitrant melter needs to be sprayed on as a "flowing coat."
That doesn't mean that there is any running or sagging where the glaze hits
the pot. It just means that glaze deposits in a continuous coating with no
granular structure. That is not at all hard to achieve as long as one
watches that wet contact point. It is also an easy way to ensure an
adequate glaze thickness. Your way (milliliters of glaze per square
centimeter of glazed surface) seems a bit over the top. Simple is
beautiful.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://iweb.tntech.edu/wpitelka/
Roger Graham on wed 5 feb 03
Vince: Further to your reservations about measuring the amount of glaze to
be sprayed, rather than just estimating by eye. "Your way (milliliters of
glaze per square centimeter of glazed surface) seems a bit over the top."
Let me try and explain.
Begin at the beginning: I'm not new to all this. Bought my first spraygun in
1961. Sprayed a lot of paint since then. Been spraying glazes
enthusiastically for 16 years, making the usual mistakes along the way. No
longer a beginner.
For starters, spraying an opaque glaze isn't usually a problem. A dribble or
a run, or a non-uniform application, just disappears into the melt. No
worse than a dribble on a dipped pot... just rub it back a bit and pretend
it didn't happen.
Spraying a TRANSPARENT coloured glaze is much less forgiving. One of my
favourite glazes is a transparent copper green. Good over carved or
sgraffito decoration. Pools in the hollows. Has to be transparent for this
effect to work. Thick coat gives dark green. Thin is pale green. But if I
DIP a large platter in this glaze. any minor dribbles show up as glaring
nasties when fired. Any attempt to rub back a dribble mark only makes it
worse.
The bigger the pot, the higher the stakes. Big pot, more likely to have a
dribble mark.
More to lose if it's not perfect. So, spraying is the way to go.
Now... how much to apply? It's not good enough just to spray by guess-work,
especially if the item is part of a matching set. Who wants a set of
three items, a dark one, a medium-green one and a pale one? To get the same
depth of colour on all pots in the set, I need to MEASURE the amount to be
applied.
Potters don't have a problem with weighing out a fixed amount of clay
every time to make a mug, or measuring the height of the mug on the wheel.Or
measuring ingredients by weight, when mixing a batch of glaze. Or firing the
kiln to a measured temperature for an expected result. What's so different
about measuring the amount of glaze to apply? It takes all of half a minute
to run a tape measure over a big pot, and make a rough calculation of its
area. And for the price of that half a minute, I can rely on getting the
right thickness every time. Not moon-rocket science, this. I've long since
found by trial and error a suitable application rate for each glaze, and
it's written on the tag label of every glaze bucket.
Is all this necessary for opaque glazes like temmoku too? For myself, yes.
Spraying a large pot, it's no big deal to calculate how much gives the
ideal finish. Could just estimate by eye (and sometimes do) but if the
stakes are higher, I measure it. Always works.
I note your preference for a wet-spot where the spray lands on the pot, as a
way of getting a flowing surface. Truth to tell, the idea scares me. No
problem on a horizontal tile or a platter, but on a vertical surface it's an
invitation for a dribble or a curtain. And while it might be evidence of an
"adequate" glaze thickness, it's not so easy to achieve a UNIFORM thickness.
Which of course matters more for a transparent coloured glaze than for an
opaque one... this is where we came in.
I'm prepared to be convinced, if it's a good method. So picture this: Tall
cylindrical pot, simple shape, same diameter all the way up. Say 25 cm high,
20 cm diameter. Transparent coloured glaze, where uniform coverage is a
must. Pot is on a turntable, in a spray booth. Away we go....
Tell how it's done. How wide would the wet-spot need to be? What happens
when you've made one complete revolution, and the wet spot overlaps where
you began? What happens when you start another revolution, one
wet-spot-width higher up or down the wall? How does one avoid a thicker
(darker coloured) band if the new wet-spot overlaps a previously applied
one? How does one avoid a thinner (paler) band if the two wet-spots don't
overlap the precisely right amount? The prospect frightens me. Do tell.
I do see the point that a "recalcitrant melter" probably benefits from a
flowing coat. Can't speak from experience at all. We have about 20 glazes in
regular use, all of them sprayed at one time or another, but most would be
fairly fluid and give no problem with surface finish if the sprayed coat is
applied smoothly with a fine spray. Matt dry glazes... we only use two or
three, and haven't really thought about it much. Just spray them on, and
they work.
You asked about kind of spray gun in use. Gravity-feed gun with the glaze
container on top, since it's so simple to measure the required volume into
the cup and spray until it's all gone. Easy to wash out afterwards... just a
quick squirt with a trigger sprayer into the cup, and spray the wash water
onto the pot
Wouldn't even consider the common suction-feed kind. Too hard to
wash, impossible to measure the quantity of fluid applied. Glaze settles out
in the pot while you work. Nasty things.
I have no experience at all with the newer High-Volume-Low-Pressure guns.
What will they do that a gravity-feed "ordinary" gun won't do cheaper? Can
you throttle them back to give a delicate narrow fan of spray, rather like
an air-brush? Can you vary the droplet size, to get different effects?
"Spatter" effects, for instance?
We've had so many visiting potters ask questions about all this when they
call in at our workshop, that I put together a glaze-spraying book some
years ago. Mostly about the care and feeding of the gravity feed gun... how
to adjust it, how to apply spray to various shapes of pot. Ideas on
measuring to get a reliable result without failures along the way. Various
ideas for a spray booth, and glaze-on-glaze spraying. Interesting things
with stencils. Not a huge venture, about 24 pages when printed out. Lots of
pictures.
I still have the complete file for the Glaze Spraying book on the computer.
Comes to almost 900 kilobytes, with all the embedded photographs, as a Word
97 document. It travels OK as an attachment to an email. Tried it... took
about 6 minutes on my slow modem, but arrived unscrambled and printed OK.
Out there in the dark Clayart jungle there may be other potters who'd like
to try some of these ideas. Not confident about spraying? Come on in, the
water's fine.
Invitation: Email me off list, if you're feeling brave, and I'll return a
message with the giant document attached. Make your own printout (about 24
pages on A4 paper). Freebie.
Best wishes,
Roger Graham, near Gerringong, Australia
http://members.optusnet.com.au/~rogergraham
Gail Dapogny on wed 5 feb 03
Dear Roger,
I always make a point to read what you have to say, and often store it!
And you helped me a lot with that binding frit with pigment question that I
had in December.
Your whole post on spraying was very interesting. I spray a lot, but seem
to get it to work successfully purely intuitively, rather than thinking out
the process. What is a suction-feed, by the way? I use a sprayer made by
Paasche which may be just that, but I don't really know. Hooked up to a
compresser.
I would like very much a copy of the Glaze Spraying book or article. Be
happy to eimburse you in any way.
Curious about your transparent copper green glaze -- is this a turquoise
sort of green?
Thanks again for all your patience and information.
Gail
>Begin at the beginning: I'm not new to all this. Bought my first spraygun in
>1961. Sprayed a lot of paint since then. Been spraying glazes
>enthusiastically for 16 years, making the usual mistakes along the way. No
>longer a beginner.
>
>For starters, spraying an opaque glaze isn't usually a problem. A dribble or
>a run, or a non-uniform application, just disappears into the melt. No
>worse than a dribble on a dipped pot... just rub it back a bit and pretend
>it didn't happen.
>
>Spraying a TRANSPARENT coloured glaze is much less forgiving. One of my
>favourite glazes is a transparent copper green. Good over carved or
>sgraffito decoration. Pools in the hollows. Has to be transparent for this
>effect to work. Thick coat gives dark green. Thin is pale green. But if I
>DIP a large platter in this glaze. any minor dribbles show up as glaring
>nasties when fired. Any attempt to rub back a dribble mark only makes it
>worse.
>
>The bigger the pot, the higher the stakes. Big pot, more likely to have a
>dribble mark.
>More to lose if it's not perfect. So, spraying is the way to go.
>
>Now... how much to apply? It's not good enough just to spray by guess-work,
>especially if the item is part of a matching set. Who wants a set of
>three items, a dark one, a medium-green one and a pale one? To get the same
>depth of colour on all pots in the set, I need to MEASURE the amount to be
>applied.
>
> Potters don't have a problem with weighing out a fixed amount of clay
>every time to make a mug, or measuring the height of the mug on the wheel.Or
>measuring ingredients by weight, when mixing a batch of glaze. Or firing the
>kiln to a measured temperature for an expected result. What's so different
>about measuring the amount of glaze to apply? It takes all of half a minute
>to run a tape measure over a big pot, and make a rough calculation of its
>area. And for the price of that half a minute, I can rely on getting the
>right thickness every time. Not moon-rocket science, this. I've long since
>found by trial and error a suitable application rate for each glaze, and
>it's written on the tag label of every glaze bucket.
>
>Is all this necessary for opaque glazes like temmoku too? For myself, yes.
>Spraying a large pot, it's no big deal to calculate how much gives the
>ideal finish. Could just estimate by eye (and sometimes do) but if the
>stakes are higher, I measure it. Always works.
>
>I note your preference for a wet-spot where the spray lands on the pot, as a
>way of getting a flowing surface. Truth to tell, the idea scares me. No
>problem on a horizontal tile or a platter, but on a vertical surface it's an
>invitation for a dribble or a curtain. And while it might be evidence of an
>"adequate" glaze thickness, it's not so easy to achieve a UNIFORM thickness.
>Which of course matters more for a transparent coloured glaze than for an
>opaque one... this is where we came in.
>
>I'm prepared to be convinced, if it's a good method. So picture this: Tall
>cylindrical pot, simple shape, same diameter all the way up. Say 25 cm high,
>20 cm diameter. Transparent coloured glaze, where uniform coverage is a
>must. Pot is on a turntable, in a spray booth. Away we go....
>
>Tell how it's done. How wide would the wet-spot need to be? What happens
>when you've made one complete revolution, and the wet spot overlaps where
>you began? What happens when you start another revolution, one
>wet-spot-width higher up or down the wall? How does one avoid a thicker
>(darker coloured) band if the new wet-spot overlaps a previously applied
>one? How does one avoid a thinner (paler) band if the two wet-spots don't
>overlap the precisely right amount? The prospect frightens me. Do tell.
>
>I do see the point that a "recalcitrant melter" probably benefits from a
>flowing coat. Can't speak from experience at all. We have about 20 glazes in
> regular use, all of them sprayed at one time or another, but most would be
>fairly fluid and give no problem with surface finish if the sprayed coat is
>applied smoothly with a fine spray. Matt dry glazes... we only use two or
>three, and haven't really thought about it much. Just spray them on, and
>they work.
>
>You asked about kind of spray gun in use. Gravity-feed gun with the glaze
>container on top, since it's so simple to measure the required volume into
>the cup and spray until it's all gone. Easy to wash out afterwards... just a
>quick squirt with a trigger sprayer into the cup, and spray the wash water
>onto the pot
>
>Wouldn't even consider the common suction-feed kind. Too hard to
>wash, impossible to measure the quantity of fluid applied. Glaze settles out
>in the pot while you work. Nasty things.
>
>I have no experience at all with the newer High-Volume-Low-Pressure guns.
>What will they do that a gravity-feed "ordinary" gun won't do cheaper? Can
>you throttle them back to give a delicate narrow fan of spray, rather like
>an air-brush? Can you vary the droplet size, to get different effects?
>"Spatter" effects, for instance?
>
>We've had so many visiting potters ask questions about all this when they
>call in at our workshop, that I put together a glaze-spraying book some
>years ago. Mostly about the care and feeding of the gravity feed gun... how
>to adjust it, how to apply spray to various shapes of pot. Ideas on
>measuring to get a reliable result without failures along the way. Various
>ideas for a spray booth, and glaze-on-glaze spraying. Interesting things
>with stencils. Not a huge venture, about 24 pages when printed out. Lots of
>pictures.
>
>I still have the complete file for the Glaze Spraying book on the computer.
>Comes to almost 900 kilobytes, with all the embedded photographs, as a Word
>97 document. It travels OK as an attachment to an email. Tried it... took
>about 6 minutes on my slow modem, but arrived unscrambled and printed OK.
>Out there in the dark Clayart jungle there may be other potters who'd like
>to try some of these ideas. Not confident about spraying? Come on in, the
>water's fine.
>
> Invitation: Email me off list, if you're feeling brave, and I'll return a
>message with the giant document attached. Make your own printout (about 24
>pages on A4 paper). Freebie.
>
>Best wishes,
>
>Roger Graham, near Gerringong, Australia
>
>http://members.optusnet.com.au/~rogergraham
>
>______________________________________________________________________________
>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.
Gail Dapogny
1154 Olden Road
Ann Arbor, MI 48103-3005
(734) 665-9816
gdapogny@umich.edu
http://www.silverhawk.com/ex99/dapogny (single historical photo - no longer
registered with Silverhawk)
Vince Pitelka on wed 5 feb 03
> Begin at the beginning: I'm not new to all this. Bought my first spraygun
in
> 1961. Sprayed a lot of paint since then. Been spraying glazes
> enthusiastically for 16 years, making the usual mistakes along the way.
Roger -
Under this situation, I will gladly defer to you. I have sprayed glazes off
an on for many years, but never as a primary part of my production. I have
helped my students with glaze-spraying problems over the years, and we have
usually achieved decent results. But I cannot say that we have ever tried
to get a very smooth overall coat of a transparent glaze, with no variation
in color. I expect your way probably works better for that sort of
application.
When we spray a glaze on a cylindrical pot as you describe, we usually spray
a spiral pattern, with each wet-spot pass slightly overlapping the previous
one. This has always given me a decent coat.
But if I wanted to get a perfectly even coat of a clear colored glaze, I'd
gladly try it your way. But I do have one more question. Once you have
measured the volume of glaze for an adequate coat, how to you ensure that
you are spraying the glaze evenly overall?
Thanks and best wishes -
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Office - wpitelka@tntech.edu
615/597-6801 x111, FAX 615/597-6803
http://iweb.tntech.edu/wpitelka/
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