Official Luthiers Forum!
http://w-ww.luthiersforum.com/forum/

Is this what people mean when they talk about witness lines?
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10101&t=51958		 Page 1 of 1
Author:  Conor_Searl [ Tue May 21, 2019 2:01 pm ]
Post subject:  Is this what people mean when they talk about witness lines?
I've heard an awful lot about witness lines and waterborne lacquer, but have never seen a clear example of what they may look like. I've been working on the assumption that these are them, but thought I'd ask to make sure. I only really ever see these lines over darker colors, which I guess makes sense, as there is no grain pattern to obscure them.
Author:  meddlingfool [ Tue May 21, 2019 2:06 pm ]
Post subject:  Re: Is this what people mean when they talk about witness li
I think so.
Author:  jfmckenna [ Tue May 21, 2019 2:21 pm ]
Post subject:  Re: Is this what people mean when they talk about witness li
Yup when you sand through one layer that's the tell tail sign. One of the reasons I gave up on water base :(
Author:  J De Rocher [ Tue May 21, 2019 3:24 pm ]
Post subject:  Re: Is this what people mean when they talk about witness li
Looks like witness lines to me. Which water borne lacquer is it? What stage are you at in the sanding/polishing in the photo?
Author:  SnowManSnow [ Tue May 21, 2019 3:47 pm ]
Post subject:  Re: Is this what people mean when they talk about witness li
Yup :)
I’d also like to know which finish you’re using. I’ve used em6000 on 2 instruments so far and haven’t had this issue


Sent from my iPhone using Tapatalk
Author:  B. Howard [ Tue May 21, 2019 6:21 pm ]
Post subject:  Re: Is this what people mean when they talk about witness li
That's them. Train your eye and you'll see them on the spruce and lighter colors too!
Author:  Conor_Searl [ Tue May 21, 2019 6:25 pm ]
Post subject:  Re: Is this what people mean when they talk about witness li
I've been brushing on Brite-tone lacquer. This is after wet sanding (400, 600, 800, 1000, 1500, 2000, 2500) before buffing and polishing.

This is a headstock repair I did on a Seagull 12 string. The lines are really only a little visible over the black, the rest of the neck seems to be fine. Now that its super level I may do another couple coats of clear on top and not sand so vigorously. I've started wet sanding with mineral spirits instead of water, I seemed to get a lot more witness lines when wet sanding with water.

I'm super new to finishing, and have found it to be probably the steepest learning curve of all the luthiery related tasks I've learned over the past few years. I've been hesitant to learn with things other than water-based as I work out of my house and have kids around, and who knows how much longer things like nitro will even be available. The big plus for me with this stuff is I can brush on a few coats in the morning in my studio/workshop and teach guitar lessons in the afternoon and not worry about paint fumes bothering any of my students.
Author:  Conor_Searl [ Tue May 21, 2019 6:51 pm ]
Post subject:  Re: Is this what people mean when they talk about witness li
Another question occurs to me. Are witness lines the result of my poor technique, or just the nature of the beast with waterborne lacquer? From reviews I've read of this product people experience a lot less (or no) witness lines than they do other water-based products. And it is supposed to behave similarly to nitro.
Author:  Pat Foster [ Tue May 21, 2019 7:13 pm ]
Post subject:  Re: Is this what people mean when they talk about witness li
They can happen whenever you sand through coats of a finish that doesn't burn into previous coats. Without a chemical bond across coats, the witness lines are the "between" layer if you will. Usually doesn't happen with nitro lacquer or traditional shellac. I've had them appear with varnish, though a light pass on the buffer took care of those.
Author:  J De Rocher [ Tue May 21, 2019 7:55 pm ]
Post subject:  Re: Is this what people mean when they talk about witness li
Witness lines are not the nature of the beast for water borne lacquers. Maybe for some of them, but in my experience, witness lines haven't been a problem using EM6000 water borne lacquer. I've sanded through to wood [headinwall] and no witness lines. I've repaired a sand through and sanded through again [headinwall] and no witness lines. I've repaired EM6000 a couple years after it was originally applied by applying new EM6000 and had no witness lines appear from level sanding and polishing.

I haven't used Bright-tone lacquer, but maybe it's sensitive to the length of time between coats. If you go over a certain length of time between coats, a new coat may not "burn in" to the previous coat. Did you have any long periods between coats?
Author:  sdsollod [ Tue May 21, 2019 8:14 pm ]
Post subject:  Re: Is this what people mean when they talk about witness li
I also use em6000 and the only time I have seen what you show in your photo is when I sanded through to shellac underneath...
Author:  Conor_Searl [ Tue May 21, 2019 8:28 pm ]
Post subject:  Re: Is this what people mean when they talk about witness li
J De Rocher wrote:
I haven't used Bright-tone lacquer, but maybe it's sensitive to the length of time between coats. If you go over a certain length of time between coats, a new coat may not "burn in" to the previous coat. Did you have any long periods between coats?


Yes? I think so. I left it as much as a week between coats I think. I don't have my records in front of me right now.
Author:  J De Rocher [ Tue May 21, 2019 8:32 pm ]
Post subject:  Re: Is this what people mean when they talk about witness li
Conor_Searl wrote:
J De Rocher wrote:
I haven't used Bright-tone lacquer, but maybe it's sensitive to the length of time between coats. If you go over a certain length of time between coats, a new coat may not "burn in" to the previous coat. Did you have any long periods between coats?


Yes? I think so. I left it as much as a week between coats I think. I don't have my records in front of me right now.


That might be where they come from. I would see if you can find an info sheet from the manufacturer and see if there are recommendations on the maximum time between coats.
Author:  phavriluk [ Tue May 21, 2019 10:04 pm ]
Post subject:  a guess
If this Seagull headplate is not going to be glossy, then sanding/buffing the final application may very well be unnecessesary. Blow on the last application and let it dry. If it looks good, stop. My guess, susceptible to correction by folks with experience.
Author:  B. Howard [ Wed May 22, 2019 5:24 am ]
Post subject:  Re: Is this what people mean when they talk about witness li
Pat Foster wrote:
They can happen whenever you sand through coats of a finish that doesn't burn into previous coats. Without a chemical bond across coats, the witness lines are the "between" layer if you will. Usually doesn't happen with nitro lacquer or traditional shellac. I've had them appear with varnish, though a light pass on the buffer took care of those.


Not necessarily true. 2K urethane and UV polyester, neither "burn" into eachother and neither will show witness marks between layers when done properly. This is a water based finish phenomena more than anything, although sloppy work will cause witness lines even in shellac or nitro.

The reason traces back to the same thing that causes the lack of clarity typically seen in these finishes, especially over darker substrates. And it was already pointed out this is where the witness lines show most as well. The mechanics of suspending acrylic, polyesters and other plastics in an aqueous solution causes an initial polymerization not present in other technologies and this is the reason for this.
Author:  Colin North [ Wed May 22, 2019 5:46 am ]
Post subject:  Re: Is this what people mean when they talk about witness li
Yes, witness lines as others have said.
I use water-based Enduro Var, and have repaired a finish sand through (headstock/neck joint area) after more than a month's drying with no witness lines after buffing.
I dry sand EV BTW.
Author:  Barry Daniels [ Wed May 22, 2019 9:07 am ]
Post subject:  Re: Is this what people mean when they talk about witness li
You are sanding too much, which is common with inexperience. You don't need to use all of those grits. And you are starting with too low of a grit. Everyone has their own schedule, but you could probably simplify the grits to 1000 and 1500 and then polish.
Author:  Conor_Searl [ Wed May 22, 2019 11:22 am ]
Post subject:  Re: Is this what people mean when they talk about witness li
Barry Daniels wrote:
You are sanding too much, which is common with inexperience. You don't need to use all of those grits. And you are starting with too low of a grit. Everyone has their own schedule, but you could probably simplify the grits to 1000 and 1500 and then polish.


Okay cool, less sanding is definitely worth a try. I'll put another couple coats of clear on the black peg face making sure to not leave it too long between coats and then sand with just those two grits.

I guess it goes without saying that to get away with less sanding you've got to start with an impeccably prepared substrate?
Author:  Colin North [ Wed May 22, 2019 11:36 am ]
Post subject:  Re: Is this what people mean when they talk about witness li
Conor_Searl wrote:
Barry Daniels wrote:
You are sanding too much, which is common with inexperience. You don't need to use all of those grits. And you are starting with too low of a grit. Everyone has their own schedule, but you could probably simplify the grits to 1000 and 1500 and then polish.


Okay cool, less sanding is definitely worth a try. I'll put another couple coats of clear on the black peg face making sure to not leave it too long between coats and then sand with just those two grits.

I guess it goes without saying that to get away with less sanding you've got to start with an impeccably prepared substrate?

When I'm working on especially the middle/latter stages of an instrument I keep hearing this voice echoing from someone on this forum -
"Preparation is key to finishing"
Author:  Conor_Searl [ Wed May 22, 2019 11:53 am ]
Post subject:  Re: Is this what people mean when they talk about witness li
Colin North wrote:
When I'm working on especially the middle/latter stages of an instrument I keep hearing this voice echoing from someone on this forum -
"Preparation is key to finishing"


Yes! No kidding. But having come to luthiery with virtually no previous woodworking experience I had no idea the weight of that comment. More than anything else it seems between preparation and measuring there are constantly layers being pulled back and new horizons of doing it better and more thoroughly.
Author:  Colin North [ Wed May 22, 2019 4:46 pm ]
Post subject:  Re: Is this what people mean when they talk about witness li
Conor_Searl wrote:
Colin North wrote:
When I'm working on especially the middle/latter stages of an instrument I keep hearing this voice echoing from someone on this forum -
"Preparation is key to finishing"


Yes! No kidding. But having come to luthiery with virtually no previous woodworking experience I had no idea the weight of that comment. More than anything else it seems between preparation and measuring there are constantly layers being pulled back and new horizons of doing it better and more thoroughly.

I hear that! gaah
Author:  Conor_Searl [ Thu May 23, 2019 11:55 pm ]
Post subject:  Re: Is this what people mean when they talk about witness li
A couple more coats of clear, with a little over 2 hours between application. Let it dry. Gently and thoroughly dry sanded with 1000 and 1500, then polished it out. Seemed to work much better!
Author:  J De Rocher [ Thu May 23, 2019 11:58 pm ]
Post subject:  Re: Is this what people mean when they talk about witness li
Nice!
Author:  Colin North [ Fri May 24, 2019 4:25 am ]
Post subject:  Re: Is this what people mean when they talk about witness li
Just the ticket!
Author:  mountain whimsy [ Fri May 24, 2019 7:31 am ]
Post subject:  Re: Is this what people mean when they talk about witness li
I'll just add that spray technique is critical, too. I feel like I'm finally laying down smooth coats that require little sanding.
Page 1 of 1 All times are UTC - 5 hours
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/