spraying glazes for the first time, any hints?

[thiamant]

Hello!

I grabbed my old spray gun that I used for 3d printed pieces and tried spraying glazes with it for my first time. I have a good air compressor so I decided to try. The spray gun might not be the best one around, it has a 0.5 mm nozzle. But I tried a small test on a broken test tile.

I'm curious as to why it came out so powdery. Is it a bad application or is it just that it looks different than dipping? I don't know how it's supposed to look anyways.

 

Thanks!

 

[Hulk]

Hello again Thiamant!

What type of gun are you using there? Typically, those spraying glazes are using an HVLP type setup - inexpensive (the cheap ones), easy to clean, less atomization\waste (larger droplets).

I've sprayed glaze just a few times (at our local JC ceramic lab), just for fun.
I thoroughly sieved, then watered down enough glaze to fill the spray gun reservoir about half way, then gave it a test shot, just a blip on a ware board - too dry. From there, a bit more water, voila, a good fan of wet, but not immediately running.
Spraying the wares, I went with a light coating, then let it dry a bit, then another coating. It's important to plan for pointing the spray fan directly at each surface, e.g. curved surfaces, under handles, etc.
The pieces I'd selected for the trial had been fitted with small triangles of tape, so I could check the thickness of the dry glaze by carefully peeling back the tape. The resultant triangles - call them accents!

Looks like your glaze film wasn't wet enough to lay down smoothly.

Tape can be a good friend, also balloons.

There are several threads here on glaze spraying - try searching "hvlp"; perhaps experienced sprayers will chime in as the day wears on...

[blackthorn]

I'm also interested in spraying glaze and slip.

Here are a few links that I've found helpful:

https://www.youtube.com/watch?v=4btURLgFOzQ

https://www.youtube.com/watch?v=L0jS2U6PPCE

https://www.youtube.com/watch?v=1LiZ7V7CNTE

https://www.facebook.com/watch/?v=1474038826090633

Tom @Hulk is right about the spray gun. Geil sells a good one for something around $40 US dollars.

 

 

[thiamant]

Im using a small gravity fed spray gun 0.5mm 1-3 bar. 200 cc. 

Maybe I shouldve added more water to the glaze. It was around 1.4 sg.

My air compressor isnt very powerful. Just 1 HP 6 L 105 l/min. Maybe not enough for an HVLP gun?

[Min]

I have sprayed a lot of glazes, it does take some time to learn how much glaze is needed for good coverage. It's common to use too little glaze rather than too much. When I first started spraying glazes I did a kiln load or two using the method outlined in this really good article by Roger Graham. By using Graham's method of measuring out the volume of glaze and doing an estimate of the surface area I found it got me in the ballpark of how much glaze I actually needed. Once I got this figured out I could then do it by eye which really speeded up the process. One thing I disagree with from Graham's article is his feeling that gravity feed spray guns are far better than siphon (bottom feeder) spray guns. My main spray guns were Critters, very few parts to clog and replacement parts available. I swapped out the glass jar for a plastic pint jar and mounted the sprayer on the lid of that. I did use gravity feed ones also, if you go this route I suggest throwing away the little screen that is found inside them. In either case a well sieved glaze is crucial. I sprayed most glazes at around 40-45psi.

Re the powdery look, some people go for a thick velvet look to the glaze to know when they have built it up thick enough, most glazes are okay like this if the glazes are well fluxed and they will smooth out during firing. If you use a stiff glaze this doesn't always happen and you can have a pebbly finish. For vertical surfaces I prefer to move the gun in closer and follow a small puddle of glaze around and up and down the pot. I would do three times round the pot total. For flat surfaces such as platters it's hard to avoid some of the powdery look but by increasing the water content of the glaze and moving the gun closer to the pot it can help. Further away the gun is the more time there is for the glaze to dry before reaching the surface of the pot.

[oldlady]

thiamant , fire that test and look at the results.

if you really want to spray glazes, make it easy on yourself.  your ceramic supplier probably has the EZE sprayer on the shelf.  it is (was) $30.   i have 4 of them and they are so simple that you will not believe how easy they are to use.   no complicated multi-part fancy spray gun.  no watering down the glaze.  spray and the glaze dries almost instantly so you can handle the piece to put it in line for the kiln.   it is a simple siphon sprayer, cleaning is just run clean water through it until finished.  no disassembly.

your compressor is the main part of the process.  you need a bigger compressor.  most air compressors are made for tools that need  very short duration air pressure.  spraying glazes involves using air for several minutes at a time.   if the compressor is too small, it will die.   i killed one the first time i used it because i was learning on my own and did not realize that a 2 gallon tank was not evough.   i got a new 8 gallon tank and used it for many years.   i now have a 10 gallon tank and use it all afternoon doing a kiln load at a time.  23x27 kiln.   i have found that spraying greenware is much easier than spraying bisque.

rant over.

[dhPotter]

@thiamant your glaze looks a little thin. The pics show a really thick application and the result. Not all glazes will be chunky looking, some will smooth out and look watery. The trick is to know each glaze's characteristics when they are sprayed - test, test, test - and pay attention to what each glaze wants, thick or thin application.

I use a Critter spray gun and 8 gallon compressor at 40 PSI. My glazes have a Specific Gravity between 1.45 - 1.57. I spray greenware. Spray in one spot till it gets wet then move on to the next spot. May need to do this 3-4 times on the whole pot with each time around getting shorter and shorter because of glaze thickness building up.  I spray nearly everything upside down on a pedestal, especially mugs, cups, and bowls. Pour the liner in mugs and cups the day before. Spraying them upside down keeps the overspray from getting into the liner. For handled pieces spray the inside of the handle first being sure to give enough glaze coverage at the connection point on the bottom of the handle. Managing the overspray is difficult. With some glazes I wipe away, using a damp sponge, the overspray before spraying the next color. You can wipe away glaze on greenware without damaging the piece, like unwanted spills when pouring the liner.

 

[thiamant]

8 hours ago, dhPotter said:

@thiamant your glaze looks a little thin. The pics show a really thick application and the result. Not all glazes will be chunky looking, some will smooth out and look watery. The trick is to know each glaze's characteristics when they are sprayed - test, test, test - and pay attention to what each glaze wants, thick or thin application.

I use a Critter spray gun and 8 gallon compressor at 40 PSI. My glazes have a Specific Gravity between 1.45 - 1.57. I spray greenware. Spray in one spot till it gets wet then move on to the next spot. May need to do this 3-4 times on the whole pot with each time around getting shorter and shorter because of glaze thickness building up.  I spray nearly everything upside down on a pedestal, especially mugs, cups, and bowls. Pour the liner in mugs and cups the day before. Spraying them upside down keeps the overspray from getting into the liner. For handled pieces spray the inside of the handle first being sure to give enough glaze coverage at the connection point on the bottom of the handle. Managing the overspray is difficult. With some glazes I wipe away, using a damp sponge, the overspray before spraying the next color. You can wipe away glaze on greenware without damaging the piece, like unwanted spills when pouring the liner.

 

These pictures show the same powery texture that I have, so most likely its just how its supposed to look. I think thickness was ok rounding 0.5mm (its a clear glaze). Will fire and post the result.

[thiamant]

Is there a reason for not using LVLP spray guns? They are supposed to be efficient too and consume less air volume.

[oldlady]

sorry, thiamant,    i did not remember that you are in Spain so you might not have ready access to my american tools.

   my objection to using High Volume Low Pressure sprayers is to the very complicated route the glaze follows to go from the holding "tank" to the pot.   when finished with the first glaze, you must clean out the tool.   it involves disassembling a multi-part design with very small parts and then re-assembling it before using another color or type of glaze.  and never put it down for a long time and forget to clean it!

simplicity saves time and makes glazing quicker than any method i know.  the tube dipping into the pint jar of glaze is large, the tip pointing to the work can be adjusted to spray whatever pattern you like and doing it on greenware is just my method to get the pot from the clay container to a sales shelf quickly.  greenware sucks up the glaze spray so fast that the pot does not have time to get wet.   waiting for wet glaze to dry before i can put it down is painful on my wrist. 

i am getting older every day and cannot spend forever on one piece.  thinking everything i make is wonderful and should be saved forever is no longer my attitude.  i can hammer a clumsy, wrong color, less than perfect piece without feeling guilty about it.

nobody has mentioned yet that you will need a respirator so you do not breathe in glaze while you work.   thankfully, they have been simplified and more available than when i started in the 1970s.  

there are not answers to everything, ceramics is an art blended with science,  and art needs to be practiced. which is another word for test, test, test and as you do, you will learn, learn, learn if you think, think, think.

 

[thiamant]

24 minutes ago, oldlady said:

my objection to using High Volume Low Pressure sprayers is to the very complicated route the glaze follows to go from the holding "tank" to the pot.   when finished with the first glaze, you must clean out the tool.   it involves disassembling a multi-part design with very small parts and then re-assembling it before using another color or type of glaze.  and never put it down

Did you mean Low Volume Low Pressure? I thought it was the opposite, that HVLP are easier to clean.

I always use a full respirator for mixing and spraying glazes. Thats a very important thing yea.

[Bill Kielb]

4 hours ago, thiamant said:

Is there a reason for not using LVLP spray guns? They are supposed to be efficient too and consume less air volume.

This may help, I have used all and the old fashioned siphon is definitely easiest to clean. Having said that HVLP uses less air than traditional and have the cup mounted above allowing gravity to assist with feeding the material. LVLP work fine as well and atomize better for less air. My experience is to pick a nozzle size that works best with your glazes and application technique, the appropriate thinning and from there a wet enough application to get the desired coverage. Definitely a learned experience.

In my use cleanup is mostly running water through the gun, but I do remove the nozzle and cup and run water though while cycling the trigger until all is clean do a bit of a hassle. I also air brush underglaze though,  so many things while not super easy are possible with spraying and hard to duplicate by other methods.

Practice with your sprayer to get the feel and results, soon it will be second nature.

[Mark C.]

The texture suface will lay flat once heated to temp-no big deal. The thickness is what will count -getting that right is the learning part

[thiamant]

2 minutes ago, Mark C. said:

The texture suface will lay flat once heated to temp-no big deal. The thickness is what will count -getting that right is the learning part

Yeah, I guess if the glaze particles are removed by barely touching the piece, this means it's too thin right?

[Mark C.]

Spraying glaze always leaves a powdery surface and will come off if not handled with care. Dipped glazes are a bit tougher.

[Mark_H]

I can't comment on ceramics, but have sprayed a few cars.  Old Lady is correct with the size of compressor for spraying.  I used a 5hp/80 gal tank for cars (overkill for ceramics.) 

You can make a smaller compressor work, with a larger auxiliary holding tank attached to your compressor tank.  They sell these, or if you can find a broken compressor with a nice tank, that can be plumbed to it using metal pipe.

That way your compressor can fill it while your not spraying and hopefully keep up while squeezing the trigger.  

 

[thiamant]

The guy who sold me the spray gun has been trying to help. He told me I don't really need a better compressor because my pieces are relatively small (for example a 20 diameter cm bowl). He told me most likely I'm having problems with my nozzle size because 0.5 mm is too short, even more if I want a thick layer of glaze applied (min 0.5mm). So he suggested trying a cheap 1.5mm traditional spray gun at 2 bar (30 PSI) before purchasing a bigger compressor because HVLP spray guns require more than 300 L /min.

What do you think?

1 hour ago, Mark C. said:

Spraying glaze always leaves a powdery surface and will come off if not handles with care. Dipped glazes are a bit tougher.

I see. Well, I just put my finger "close" (didn't even apply pressure) to the piece and almost all the layer went off.

[dhPotter]

The sprayed glaze needs to have clay and/ or bentonite to help it stick to the pot.

I never tried this but maybe a bit of brushing medium added to the glaze would help stick it to the pot.

[thiamant]

20 minutes ago, dhPotter said:

The sprayed glaze needs to have clay and/ or bentonite to help it stick to the pot.

I never tried this but maybe a bit of brushing medium added to the glaze would help stick it to the pot.

This glaze contains 20% kaolin.

[Magnolia Mud Research]

two articles addressing spray equipment is available on  Vince Pitelka's website:    
https://vincepitelka.com/wp-content/uploads/2019/03/Spray-Equipment-and-Compressors.pdf 

https://vincepitelka.com/wp-content/uploads/2016/03/Using-the-Gravity-Feed-HVLP-Spraygun.pdf 

My experience with spraying glaze requires a slurry that is "less viscous" than dipping/pouring glaze slurries, which generally means more water and lower specific gravity. 

Also remember to always stand upwind of the ware when spraying.

LT
 

[Min]

4 hours ago, thiamant said:

So he suggested trying a cheap 1.5mm traditional spray gun at 2 bar (30 PSI) before purchasing a bigger compressor because HVLP spray guns require more than 300 L /min.

If you look at the siphon feeding Critter or EZE sprayer or the Bailey rebranded version of the Critter they use approx  2 C.F.M. @ 30-90 P.S.I. or in metric  approx 56 litres per minute. Problem with too small a compressor is you will be standing around waiting for it to recharge longer than you will be spraying a pot for.

I don't get the powdery look on vertical surfaces unless I have the gun too far away from the pot. The drier the glaze is as it hits the pot the more powdery it will be. There is a balance between having a low enough specific gravity to create a wet puddle of glaze that you "paint" on with the gun and yet not so low as the glaze takes too long to dry or excessively wets the pot causing runs or blistering.  You can add gum to toughen up the surface but it will slow down the drying time but I've never found it necessary when the glaze contains enough clay.

edit: As well as a respirator a comfortable pair of hearing protection ear muffs is a good idea while spraying.