Applying barium sulfate coatings
Bughunter
in a calibration fixture for a wide field of view imaging
spectrometer. The chosen diffuser material is the Edmunds Industrial
Optics p/n NT53-697 Barium Sulfate reflection coating.
I was wondering if anyone can share experiences or tips using these
kinds of BaS coating spray applicators, especially any hints as to
application techniques and curing methods.
Thanks in advance.
Rick.
Mark W. Lund, PhD
http://www.aviantechnologies.com, or if is too big to get into
a truck, consult with him.
There are a lot of subtleties to coating a sphere, it may be
worth while to get an expert to help you.
Best regards
mark
--
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Mark W. Lund, PhD ** Custom Battery Chargers
CEO ** Bulk Cells and Custom Battery Packs
PowerStream Technology ** Custom Power Supplies
140 S. Mountainway Drive ** DC/DC Converters
Orem Utah 84058 ** Custom UPS
http://www.PowerStream.com ** Custom power management electronics
Brigham Young University Alumni e-mail: lu...@xray.byu.edu
Arfty1166
>Personally, I would send sphere to Art Springsteen
>http://www.aviantechnologies.com, or if is too big to get into
>a truck, consult with him.
>
>There are a lot of subtleties to coating a sphere, it may be
>worth while to get an expert to help you.
>
>Best regards
>mark
>
>Bughunter wrote:
>> We are building a segment of a large radius spherical diffuser for use
>> in a calibration fixture for a wide field of view imaging
>> spectrometer. The chosen diffuser material is the Edmunds Industrial
>> Optics p/n NT53-697 Barium Sulfate reflection coating.
>>
>> I was wondering if anyone can share experiences or tips using these
>> kinds of BaS coating spray applicators, especially any hints as to
>> application techniques and curing methods.
>>
>> Thanks in advance.
>>
>> Rick.
Hi All,
No, I didn't pay Mark for the plug but do appreciate it! There are some
subtleties involved with coatring- proper surface prep (sandblasted surfaces
help, but they need to be well cleaned thereafter), flow rate and air presure
in the spray gun, rate of application and time between coats, just to start all
can affect the quality of the surface and the reflectance. If I were to give
one major hint, it would be to be patient and put the coating on in many coats,
rather than a few. You should have a final thickness of about 0.4 to 0.5 mm.
(16-22 mils, actually- whatever that translates to in metric- we recommend the
metric dimensions I gave) and it should take 16-25 coats. Yes, that many. And
yes, it WILL take quite a while.
BTW: with due respect to Edmunds (and the coating they sell is one I
developed), those applicators suck! (Sorry!) You really need professional
spraying equipment to do a good job, although (truth be told) we used to do a
very good job using Wagner power painters... I would hate to have to even try
to do a large surface using the Edmunds applicators. Sorta like painting your
car with cans of Krylon...
Best regards,
Art Springsteen PhD
Avian Technologies LLC
Elliot Burke
Edmund stuff is. Considering the relatively low cost of the paints compared
to time required for project, wouldn't you rather have paint from a company
in the business of making integrating spheres?
Consider that the paint is BaSO4 and PVA binder. PVA is basically white
glue. What you learned in grade school about white glue may come in handy.
First of all, make sure the surface you are painting is not water sensitive
(won't rust).
Some tooth on the surface for adhesion will be good, I used an acrylic
primer. Artists acrylic gesso would probably be better.
Conventional air brushes and small air spray tools didn't work for me.
The Wagner buzzer type sprayer worked fine.
Lots of thin coats, build up the the desired thickness.
To find out if the layer is thick enough, make a witness piece to paint at
the same time as your good part. Paint half of the witness black, the other
half white. After enough layers are on so that you can't tell the
difference between the white and black primed halves, put a couple more
coats on for good measure.
The (dry) paint layer is brittle. Small repairs can be done with a cotton
swap soaked in paint. Once more, lots of layers.
regards-
Elliot Burke
"Bughunter" <cross_...@yahoo.com> wrote in message
news:1f1d178b.03101...@posting.google.com...
Arfty1166
>I coated a few spheres with labsphere paint. Don't know how similar the
>Edmund stuff is. Considering the relatively low cost of the paints compared
>to time required for project, wouldn't you rather have paint from a company
>in the business of making integrating spheres?
>
>Consider that the paint is BaSO4 and PVA binder. PVA is basically white
>glue. What you learned in grade school about white glue may come in handy.
>
>First of all, make sure the surface you are painting is not water sensitive
>(won't rust).
>
>Some tooth on the surface for adhesion will be good, I used an acrylic
>primer. Artists acrylic gesso would probably be better.
>
>Conventional air brushes and small air spray tools didn't work for me.
>
>The Wagner buzzer type sprayer worked fine.
>
>Lots of thin coats, build up the the desired thickness.
>
>To find out if the layer is thick enough, make a witness piece to paint
>at
>the same time as your good part. Paint half of the witness black, the other
>half white. After enough layers are on so that you can't tell the
>difference between the white and black primed halves, put a couple more
>coats on for good measure.
>
>The (dry) paint layer is brittle. Small repairs can be done with a cotton
>swap soaked in paint. Once more, lots of layers.
Couple of points:
1) The Edwards paint is the Labsphere coating. And it is expensive.
2) PVA is not the same as white glue. It's the same as the adhesive on the old
'lick and stick' postage stamps.
3) You can coat perfectly well over aluminum. Use of a primer is not usually
either necessary or recommended. You can solubilize some of the binder in the
primer and it will leach upwards, causing the coating to yellow sooner.
4) An air brush will work if the coating is well blended before use. Yes, a
Wagner sprayer works just fine.
5) paint is indeed brittle. Actually, small repairs can be done with a q-tip
moistened with distilled water (especially if you have bubbles ), then uses a
fine artist brush to fix any 'oopsies'.
Best regards,
Art Springsteen
Avian Technologies LLC
Elliot Burke
"Arfty1166" <arft...@aol.com> wrote in message
news:20031017150857...@mb-m04.aol.com...
expensive compared to hardware store paint, but not expensive compared to my
time. If I was making integrating spheres in quantity and used gallons of
the paint the price would matter.
Over the last four years I've make a few integrating spheres and repaired a
few with the same bottle of paint. The pain of first cost is long gone.
Its funny how little BaSO4 costs commercially. I wonder if the integrating
sphere paint is expensive because of some extraordinary purity required, or
maybe they just make a profit.
I've made lots of paint for artistic purposes, it's very simple. You make a
little mill and grind oil and pigment together, the ways its been done for
centuries. Just as good as the expensive stuff in the tube, better than
most, at a small fraction of the price. Pastels and water color are even
easier. Gum arabic or gum tragacanth are the binders.
> 2) PVA is not the same as white glue. It's the same as the adhesive on the
old
> 'lick and stick' postage stamps.
No. The old Elmers white and some other brands white glue were mostly PVA..
Not the carpenters glue, that's something else. Lots of people use dilute
white glue for various craft applications, as a replacement for PVA. A
google search on "PVA white glue" will give lots of hits. .
> 3) You can coat perfectly well over aluminum. Use of a primer is not
usually
> either necessary or recommended. You can solubilize some of the binder in
the
> primer and it will leach upwards, causing the coating to yellow sooner.
Right. But I've coated over steel, and it was necessary to use a primer.
Most primers will not soften after hardening. Wouldn't be much use if they
did. A good point though. Make sure to use a primer that resists water
well, if you need one. There are probably some interior duty only primers
that could have the problem you describe.
Without primer the steel rusted and in a few days the coating was rust
colored. Off it came, on went the primer. Should have started with
aluminum.
> 4) An air brush will work if the coating is well blended before use. Yes,
a
> Wagner sprayer works just fine.
Maybe I was too impatient with the air brush. A little paint came out, but
to get a mm thick layer on a 300 mm diameter sphere would have taken a week.
Probably would be fine for very small jobs or some touch up.
> 5) paint is indeed brittle. Actually, small repairs can be done with a
q-tip
> moistened with distilled water (especially if you have bubbles ), then
uses a
> fine artist brush to fix any 'oopsies'.
>
Won't the surface be slicker, a bit less diffuse after you brush it with
water? The spray gun left a nice matte surface.
What would you think of mixed BaSO4 with a bit of gum tragacanth & water to
make a paste- like the first step in making pastels. It could be molded to
any shape desired and will dry out in a few days. Make some small
integrating spheres that fit detectors & fiber ferrules exactly. This would
contain some sort of armature for durability. (Maybe PVA would be better
than gum tragacanth, it would take a bit of experimentation)
Another lover of goopy craft processes,
Elliot Burke
Phil Hobbs
> 2) PVA is not the same as white glue. It's the same as the adhesive on the old
> 'lick and stick' postage stamps.
Postage stamp glue is made from potato starch.
Cheers,
Phil Hobbs
Arfty1166
>> 2) PVA is not the same as white glue. It's the same as the adhesive on
>the old
>> 'lick and stick' postage stamps.
>
>Postage stamp glue is made from potato starch.
Phil,
Hmmm. I collect stamps and read Linn's Stamp News, That's where I got that
info. The more recent stamps used PVA. Potato starch, after getting slightly
wet, ferments. PVA also does, albeit at a slower rate.
cheers!
Art S.
Arfty1166
>> Couple of points:
>> 1) The Edwards paint is the Labsphere coating. And it is expensive.
>
>expensive compared to hardware store paint, but not expensive compared to
>my
>time. If I was making integrating spheres in quantity and used gallons
>of
>the paint the price would matter.
>Over the last four years I've make a few integrating spheres and repaired
>a
>few with the same bottle of paint. The pain of first cost is long gone.
We also make and sell barium sulfate coating. Ours is a lot cheaper than the
Labsphere/Edmunds stuff (which, BTW, I developed...). It is expensive. That's
what our customers tell us (they say that about ours, too!). But thjey're sued
to paying for Krylon...
>
>Its funny how little BaSO4 costs commercially. I wonder if the integrating
>sphere paint is expensive because of some extraordinary purity required,
>or
>maybe they just make a profit.
>I've made lots of paint for artistic purposes, it's very simple. You make
>a
>little mill and grind oil and pigment together, the ways its been done for
>centuries. Just as good as the expensive stuff in the tube, better than
>most, at a small fraction of the price. Pastels and water color are even
>easier. Gum arabic or gum tragacanth are the binders.
Ah yes, everyonme thinks it's simple. And it is simple to make really crappy
coating. We spent months getting avendor who consistently supplied barium
sulfate with teh right optical properties. And it ends up NOT being the
'purest' material available. It's a combination of factors taht make the best
pigment.
>
>> 2) PVA is not the same as white glue. It's the same as the adhesive on
>the
>old
>> 'lick and stick' postage stamps.
>
>No. The old Elmers white and some other brands white glue were mostly PVA..
>Not the carpenters glue, that's something else. Lots of people use dilute
>white glue for various craft applications, as a replacement for PVA. A
>google search on "PVA white glue" will give lots of hits. .
Point well taken. But use that as a binder and i guarantee the coating will
yellow fairly quickly. Again, it's using the right PVA and preparing it
correctly.
>
>> 3) You can coat perfectly well over aluminum. Use of a primer is not
>usually
>> either necessary or recommended. You can solubilize some of the binder
>in
>the
>> primer and it will leach upwards, causing the coating to yellow sooner.
>
>Right. But I've coated over steel, and it was necessary to use a primer.
>Most primers will not soften after hardening. Wouldn't be much use if
>they
>did. A good point though. Make sure to use a primer that resists water
>well, if you need one. There are probably some interior duty only primers
>that could have the problem you describe.
>Without primer the steel rusted and in a few days the coating was rust
>colored. Off it came, on went the primer. Should have started with
>aluminum.
Yes, steel needs a primer. But we see mostly aluminum and plastics to coat. We
recommend against using steel.
>
>> 4) An air brush will work if the coating is well blended before use. Yes,
>a
>> Wagner sprayer works just fine.
>
>Maybe I was too impatient with the air brush. A little paint came out,
>but
>to get a mm thick layer on a 300 mm diameter sphere would have taken a week.
>Probably would be fine for very small jobs or some touch up.
You need to blend the coating very well to use an air brush. otherwise it will
clog up.
>
>> 5) paint is indeed brittle. Actually, small repairs can be done with a
>q-tip
>> moistened with distilled water (especially if you have bubbles ), then
>uses a
>> fine artist brush to fix any 'oopsies'.
>>
>Won't the surface be slicker, a bit less diffuse after you brush it with
>water? The spray gun left a nice matte surface.
True, a spray will be better but for just fixing bubbles, a wet q-tip works
fine. Oh, no- DON'T BRUSH!!! Just touch the bubble, which will collapse and be
diffuse.
>
>What would you think of mixed BaSO4 with a bit of gum tragacanth & water
>to
>make a paste- like the first step in making pastels. It could be molded
>to
>any shape desired and will dry out in a few days. Make some small
>integrating spheres that fit detectors & fiber ferrules exactly. This would
>contain some sort of armature for durability. (Maybe PVA would be better
>than gum tragacanth, it would take a bit of experimentation).
I would think that gum traganth would be a decent binder BUT would likely not
be UV stable. Again, ya gets what youse pay for... Is there a better barium
sulfate coating out there than ours or Labsphere's? Maybe, but I haven't seen
it. I just got some data from a company in Italy who make a competitive coating
and it's almost (almost) as good. But, the reality is that no matter how good
the coating, you've got to apply it correctly or all bets are off...
Oh, wait a second- you want to make a plastic... Doesn't work. barium sulfate
is actually somewhat translucent- doesn't cover like something like titanium
dioxide. You can put it into a fluorocarbon like PTFE (see one of my patents on
this one...), but that is very expensive.
>
>Another lover of goopy craft processes,
Yeah, nothing like white goopy processes to make your day!
>
>Elliot Burke
Cheers!
Art Springsteen
Phil Hobbs
Dunno. I got the info by listening to the USPS guy in charge of finding
a new adhesive, who was interviewed on NPR about three years ago.
Cheers,
Phil Hobbs
Elliot Burke
completely benign. A good reason to make kid's glue from it rather than
something else. One compounded form had mercuric sulphide (!!) in it. They
still referred to it as PVA. In fact a great many compounded forms of PVA
are available. Some probably are more stable and less likely to yellow than
others.
Art, I can easily believe that purity of materials and particle size have
great influence on paint and its durability. A New York painter in the 50's
used mayonnaise as a medium. Guess what his paintings look like now?
The question is, are we paying for the purity or the knowledge? Not that
I'm averse to paying for either one.
Perhaps you know why BaSO4 is used rather than some higher index of
refraction solid?
As for the durability of gum tragacanth, there are pastel paintings made
from it centuries old that aren't falling apart. Pastel is known for not
yellowing, unless someone sprays shellac or varnish on it.
regards-
Elliot Burke
"Phil Hobbs" <pc...@SpamMeSenseless.us.ibm.com> wrote in message
news:3F949810...@SpamMeSenseless.us.ibm.com...
Arfty1166
...
>The question is, are we paying for the purity or the knowledge? Not that
>I'm averse to paying for either one.
>
>Perhaps you know why BaSO4 is used rather than some higher index of
>refraction solid?
Hello all,
Actually, the answer to the first is a bit of both. None of the components are
all that expensive and it's not totally rocket science to make the stuff but
there are some tricks and coating agents that make it work a lot better.
Why barium sulfate? High reflectance over a very wide region of the spectrum-
you could use zirconia or even alumina but barium sulfate is good well down
into the UV and pretty far up into the NIR. Plus it is relatively cheap and
readily available and non-toxic. All good things!
Point taken on gum traganth but I think it would not make a good coating
binder. But I've been wrong before. Is it water soluble? Ah, yes- it's a
polysacchride of mannose and galactose, so sayeth my 30 yr. old Merck Index,
and completely water soluble. That may be a limiting factor in its use as a
binder. You want something that isn't really soluble in water at all temps, as
Guar gum (the other name for tragacanth) is. Interesting thought, tho!
On the PVA question- the better stuff you buy, the better the coating. But it's
a tradeoff on the MW you buy as to the properties of the coating...
Cheers!
Art Springsteen