Tiny bubbles in varnish

Construction and repair of Classical Guitar and related instruments
amezcua
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Tiny bubbles in varnish

Post by amezcua » Tue Nov 28, 2017 9:51 pm

Bubbles and dust are a nightmare when using varnish . Neat varnish is just too difficult . Diluting varnish about 1 varnish to 4 white spirit is much easier. Brushing on thinly and then wiping off the excess ----avoids ----building up a thick layer .That does not seem to create any dust fibre spikes . Tiny bubbles are the thing to watch out for. After a number of micro thin varnishings I flattened the surface with a small wooden block wrapped in cotton cloth with sunflower oil and fine pumice powder .That cleaned off easily with white spirit .
I was aiming to get a reasonable gloss without lots of rubbing and polishing .I think I found the answer yesterday . I made a 1 varnish to 4 white spirit dilution and inspected the mixture slowly with the brush . I shifted every tiny bubble to one side and waited till they popped. I had previously been applying varnish in a crisscross way similar to painting a door . That`s all wrong . This time with no bubbles in sight I slowly trailed the brush in a low angle along the back with the hairs pointing backwards. If the hairs are working sideways any springing back of the fibres is likely to create bubbles. I wanted the varnish to flow off the hairs with no disturbance. Keeping the brush in contact was important. Any turning had to be done slowly ,without bending the brush hairs. Lifting off to pick up more varnish happened at the edges.No pressure or flicking allowed .
So that was my method . It does seem to have worked. The lovely mahogany grain shows through clear varnish . The original dry wood texture is still visible in the varnished surface. I made no attempt to grind it all into one glassy smooth surface. This is a very lightweight guitar and the back has been completely refinished . I took off the scruffy and dirty original coating as there was area running right round that had peeled off .Two long cracks with dirt were cleaned and glued.This looks like a happy , beautiful guitar again . The top varnish is still as it was with minor repair spots .

Alan Carruth
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Re: Tiny bubbles in varnish

Post by Alan Carruth » Wed Nov 29, 2017 6:50 pm

Varnishing technique is certainly tricky, and takes time to acquire. Wait until you try a violin: I have a few choice words for the guy who came up with the idea of putting highly colored varnish on a violin scroll.

Some of the 'dust' you see in varnish is actually what they call 'sand'. It's tiny particles of varnish that didn't get cleaned out of the brush and dried there. It's certainly a nuisance if there's a lot of it, but, on the other hand, it's varnish, after all. If it's not too bad I usually just knock the peaks off with fine sanding and varnish over it.

amezcua
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Re: Tiny bubbles in varnish

Post by amezcua » Wed Nov 29, 2017 9:35 pm

I found a number of sites today that do just what I discovered yesterday . One demonstration was on an oblong table and he only used dead straight strokes. I used a bristle brush which is right for oil based varnish . My final coat has a minute bobbly texture and I think that was caused by tiny bubbles in previous cats that left minute hollows .I think the effect is very pleasant so I will keep it like that . I have not really touched the sides yet . I wiped any excess around the edges onto the sides but the sides will be done a little better as I have some tiny experience now .
I thought the varnish video was funny when he sanded with a monster machine throwing dust everywhere . None of the video showed much cleaning apart from the tack rag .That was useful .
One good tip was to avoid letting the bristles flick anywhere as that creates bubbles between the hairs . He was very keen on brush cleaning but I prefer to use a new brush at present . I do wash "the brush "after each coat though .
One of the big points I have not achieved yet is to use a top quality fine haired finishing brush . I think that would get me where I want to be . All these good tips could get a young entrepreneur a profitable sideline or permanent job . Very satisfying when it works right . The back of this guitar had been damaged with a vertical drop and caused two cracks .The section between the cracks had been glued back but you could see two ridges where the new glue had raised the surface . It was stable and so I kept it as it stood and wanted to avoid any sanding . I am using coarse and fine pumice powder with a cotton covered block of wood . I coat the surface with oil first and add pumice as each new area is rubbed .
The guitar works as it is ,so no need to take the back off . Three rather hefty cleats had been glued inside so it will be pretty secure .
Last edited by amezcua on Thu Nov 30, 2017 7:24 pm, edited 1 time in total.

amezcua
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Re: Tiny bubbles in varnish

Post by amezcua » Thu Nov 30, 2017 7:21 pm

Sometimes you see a video but much later a question pops up . In one of the varnishing videos there is good advice about laying it on thin . The varnish is partly diluted by 25% thinner . But look at the brush being used . It looks about 4 inches wide and is a full and bushy type . Not a thin and slender one. Is there a wide ,thin , fine haired varnish brush ? Surely the brush dimension will affect the "laying on thin " process . Answering my own question I think the lightness of contact is crucial to laying on thin . I forgot to pass on a good tip .For solvent based varnish they recommend Hog hair . Split ends on the hairs is a plus .Don`t attack them with the scissors . I think badger hairs are good .Also buffalo hair , which grows in their ears . That`s expensive for obvious reasons if you think about it .

Ryeman
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Re: Tiny bubbles in varnish

Post by Ryeman » Sat Dec 02, 2017 1:14 pm

I'm not sure if it is a good idea to thin varnish out as much you did. 1part varnish to 4 part thinner runs the risk, I think, of taking too much adhesion out of the varnish, though I must stress that I am no expert in this matter, and don't actually know which varnish you are using. But I do understand the problem you have described with bubbles. This problem caused a lot of discussion on a traditional fishing forum once, where cane rod restorers were getting bubbles when varnishing cane rods. I had this problem myself. I didn't entirely solve it, but warming the varnish helped. It makes it more runny, without having to dilute it so much to get the same viscosity. Varnishing in a warm room also helps. And the type of brush is important. I got good results with a squirrell hair mop, that has quite soft bristles. Technique is also important, as you have discovered.

Alan

Pat Foster
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Re: Tiny bubbles in varnish

Post by Pat Foster » Sat Dec 02, 2017 4:27 pm

I found that I could reduce the sand that Alan Carruth mentioned by using a brush spinner when cleaning the brush.

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henry dumay
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Re: Tiny bubbles in varnish

Post by henry dumay » Mon Dec 04, 2017 2:20 am

Was'nt there a song by that name??
2000 Olivo Chiliquinga Grand Concert (Equador)

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Beowulf
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Re: Tiny bubbles in varnish

Post by Beowulf » Mon Dec 04, 2017 3:24 am

henry dumay wrote:
Mon Dec 04, 2017 2:20 am
Was'nt there a song by that name??
Yes, by Don Ho! Ho! Ho! :noel:
1971 Yamaha GC-10

amezcua
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Re: Tiny bubbles in varnish

Post by amezcua » Wed Dec 06, 2017 9:46 pm

I had a very cheap set of brushes in a plastic package. Then I read about better quality Hog Hair brushes So I ordered one to see the difference.Meanwhile in looking for brush information I came across a shaving site discussing Hog Hair versus Badger . More shaving information than you will need in 5 lifetimes but it gave an insight into what Hog bristles are all about . That mentioned split ends too . So my new brush arrived and comparing that to my cheap set there is no difference. Magnified pictures of bristles show them to be just the same. The confusing part is the cheap set printing on the package says in smaller print "Synthetic bristles for good finish ". But they are not synthetic! They are just Hog Hair. They were £1.99 a packet. The single brush was £3.22 .It is a slimmer brush . The pack brushes are twice as thick . The shaving site ( there are several of them so I can`t find the one I mentioned ) tells you how a hog hair brush improves with months of use . Badgers don`t need running in .(Who knew that ?) The single brush was from Turner and Gray. I got it in Home Bargains . Extra Value Pack. Strangely there is a legal loophole for shops that add the word Value. That means they can chuck all kinds of rubbish in the product . That applies to food mainly . Brushes are probably fine .

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Michael.N.
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Re: Tiny bubbles in varnish

Post by Michael.N. » Wed Dec 06, 2017 11:03 pm

Hog/boar bristle is used a lot for paint and oil varnish. It's a relatively stiff brush with good spring, which is appropriate for thicker mediums. The split ends help with varnish loading. If you are thinning the varnish a lot then you might be better off with softer finer bristle such as a cattle/ox hair brush, often used by violin makers for their oil varnishes. I have an Omega lily white hog hair brush but I much prefer the ox hair for the varnishes that I use. Thinner mediums such as spirit varnish require even softer hair, something like hake or squirrel.
Historicalguitars.

amezcua
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Re: Tiny bubbles in varnish

Post by amezcua » Thu Dec 07, 2017 5:36 pm

Ladies` makeup brushes have some very fine hair . Hair and bristles are the division there. I would also like to know which varnishes are incompatible where one (unknown )type is dry and another is being applied on top . One of my guitars had a thick leathery jacket of varnish that I removed with varnish remover . The area just round the bridge seems reluctant to accept anything much . As if just varnishing was not difficult enough . Violins are not finished with French Polish as it would be awkward and not durable enough under a bridge . Some violin makers claim they follow the Stradivarius method but they still varnish underneath the fingerboard which did not happen originally . That indicated that the violin was set up with the much lower fingerboard on before the top was varnished . But they fit the purfling before the plates are glued on. That was not the Italian way either . Violins are rubbed down after varnishing with Pumice powder and then Tripoli and after all that they cheat and pop on a little wax to make it all shiny .

amezcua
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Re: Tiny bubbles in varnish

Post by amezcua » Fri Dec 08, 2017 3:52 pm

Today I am very happy about progress with the varnishing . I varnished two guitar tops. I only do one side of a guitar at a time and keep it horizontal . The new brush was one inch wide and slimmer than a normal paint brush . Under 1/4 inch thick . I improved my varnishing technique by reducing the disturbance in the brush hairs. I can still improve on this when I reload the varnish . I realised that taking on fresh varnish should be done slowly with the bristle tips starting in shallower varnish to allow the liquid to be drawn up by capillary action , mainly to move any bubbles hiding between the bristles to rise away from the tip .
Some of my brushing angles on the tops were still a bit vertical. A nice flat brush angle should be aimed at. I still need to get a decent reflection as I apply the varnish so I achieve a clean overlap on the previous stroke . .Finding narrow bare strips is a trap to avoid . Maybe I should crouch over the brush the way tv chefs prepare their food .
Any rubbing down between coats can be done with oil and fine pumice or tripoli but one fairly successful ingredient for the final shine was toothpaste. They even gave a list of different toothpastes for comparison .
Badger or other animal hairs are much finer with less room for bubbles so that could be a way forward .
Overall the latest two attempts have been a remarkable improvement caused by paying so much attention to my brushing methods .
I wanted to avoid discussions about the exact varnish I use but this is about solvent based varnish . The articles about wiping varnish tell us that dilution is not a problem . Use as much white spirit or Sanodor as you choose . It will not cause a problem .
Bottom line is to keep the total of all the varnish layers as thin as you can . The fewer the better .
I may have dragged out the detail here but if you look at shaving sites it`s a drop in the ocean .

amezcua
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Re: Tiny bubbles in varnish

Post by amezcua » Sun Dec 10, 2017 12:15 am

After reading an article about polishing varnish using toothpaste (from a violin based site ) I tried it myself. I dispensed with their more complicated mixtures and had a small bowl of lukewarm water and some green washing up detergent for lubricating the toothpaste. I used a small wooden block 4cms X2cms X 1 .5 cms (thick ). This was wrapped in piece of a white cotton T shirt . I dipped the block in the soapy water and applied a small squirt of toothpaste . Rubbing with the grain soon smoothed out the small amount of tiny dried bubbles . The toothpaste does not create any dull patches as fine pumice would do .After a thorough rubbing all over I wiped off the toothpaste and then rinsed off the detergent with clean water and tissues . Then dried the surface and rubbed it all dry to see how it looked .
Notes about varnishing ; The only parts that needed any more attention were slight vague imprints from the tip of the varnish brush that had been started in the centre of the top . I can clearly remember where those touches happened .
The tricky areas for starting and stopping are around the bridge .The game is to try to use only straight strokes . Some covering protection for the label inside the guitar should be in place . Stopping at the bridge is a bit awkward so -----start at the bridge rather than the edge and brush towards the soundhole in a straight line. Carefully overlap the previous stroke by an eighth of an inch and don`t let the brush flick when you get to the hole . That soundhole to bridge area can be done in straight lines and then try to brush from the outer bridge parts all the way to the top edges. After that you have nice long runs each side just past the bridge ends to the bottom. The area below the bridge is then done in a similar way . Bridge down towards the edge . The outer bout curves just need gentle brush handling but none of that had caused any problems .
The violin site report about toothpaste polishing of varnish sounded as if they had not diluted the varnish .That showed up in the comments list of the results . (Mainly the word Lumpy )
One more coat of thinned varnish with the new brushing strategy should give a superb result after the final polishing. The clarity and smoothness are impressive .
The violin site mentioned cloudiness for one test .They were mixing up solvents , water and oils so I would expect that to end up with an emulsion. Keep it simple .
My toothpaste was Colgate cool stripe .
It might be good idea to have 2 or 3 brushes ready in case you have disturbed any brush hairs too much .
Next move is to learn about really fine brush hairs .

amezcua
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Re: Tiny bubbles in varnish

Post by amezcua » Sun Dec 10, 2017 12:50 pm

A Redtree Badger Hair brush (Chinese Badger ) is on it`s way from the Boatpaint company .One inch wide and shaped like a chisel with a brass ferrule. Handle is pencil style. I hope that works rather than a flat handle. It may reduce lifting or twisting movements . The shaped chisel style will make a standing start at the edge of the bridge a lot tidier . Also I ordered some tack rags . The cheaper ones have a light coating of some adhesive . The pricier ones are made with every fibre coated in a non drying resin . Oh no! Don`t like that . The cheap ones sound better for this job . Also ordered were some varnish filters to take out any unwanted lumps or bits .
The first site I saw advising about varnishing with brushes has a photo of the writer using his brush . I`m getting ultra picky now but his brush is still too upright and he is bending the hairs . (Edit here; He is also brushing right to left with the right hand . No. Back strokes only is best ).Try to aim for a 20 degree brush angle and minimal hair bend. If you brush in both directions any bubbles rising out of the hairs will be ready to stick to the surface as you change direction . I just thought of that .
The application strategy has moved forwards overnight . I realised the guitar needs to be placed the right way round for the strokes. For right handers ; Get the tuners placed to the right side of you . Starting with the bridge -to- soundhole stroke , the chisel shaped brush , making a clean start ,will move to the right . Keep it going like that for the side nearest you . Try not to reach across any wet varnish . Gradually work towards yourself . This means beginning the bridge strokes right at the far side of the bridge . That has to be the most awkward one as the soundhole and fretboard can become obstacles. Anyway work towards yourself till the edge and then turn the guitar round so the tuners are on your left . Fill in the area below the bridge first and then fill up the long stretches from top to bottom of the guitar body . Just keep a low brush angle and straight lines with a slight overlap . Lifting off the brush will not leave a dry trace like beginning brushing in the middle of the top .Come in from the edge if you have to do a fill in .
Trying to be ultra careful seems to make my hand a bit shaky but that was probably trying to brush from right to left . Only brush from left to right . For tennis fans just do back hand strokes .
A shaky hand does not show up with diluted varnish .One tiny bonus for trying so hard .
For sinistrals these hints will be vicky vercky .

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