Varnish help request

[J M Pryor]

I am having some bubbles come up in my home cooked copal 50/50 BLO varnish. It seems fine until I mix in turpine or mineral spirits upon which it starts bubbling. I mulled some with a lake the other day and after cure it looked as if it was sandpaper. Any ideas on what might cause this?

 

[joerobson]

13 hours ago, J M Pryor said:

I am having some bubbles come up in my home cooked copal 50/50 BLO varnish. It seems fine until I mix in turpine or mineral spirits upon which it starts bubbling. I mulled some with a lake the other day and after cure it looked as if it was sandpaper. Any ideas on what might cause this?

 

Pictures?

[Nick Allen]

Also did you start with BLO? Or did you boil cold pressed pure linseed oil to start with?

[J M Pryor]

I started with cold pressed Linseed oil. I washed it in a 1 liter bottle about 1/4 full of water and 1/2 of oil. Let this sit in the window for about a week. Then cooked with raw umber pigment added with a light smoke for a couple hours. Pretty much following the article in the Strad not too long ago.

I had originally said copal and it was colophany cooked up with the B L O

 

Edited August 11 by J M Pryor
Additional information

[Anthony Panke]

Do you shake the varnish/are you rough when mixing it?

I would think air gets in when mixing 

[J M Pryor]

14 minutes ago, Anthony Panke said:

Do you shake the varnish/are you rough when mixing it?

I would think air gets in when mixing 

A careful stirring. The bubbling appears and if I knock it down with a brush or stir them back out they seem to reappear. It's as if there's something chemically going on.

 

[Michael Szyper]

1. Most common: not properly filtered

2. Often the highly fugitive solvents make bubbles because of a too fast evaporation. Add a slower evaporating solvent, for example spike oil (a tiny bit is enough) or lamp oil.

3. Worms due to not sufficiently washed linseed oil. I would use a good quality  oil and wash it properly

[J M Pryor]

8 minutes ago, Michael Szyper said:

1. Most common: not properly filtered

2. Often the highly fugitive solvents make bubbles because of a too fast evaporation. Add a slower evaporating solvent, for example spike oil (a tiny bit is enough) or lamp oil.

3. Worms due to not sufficiently washed linseed oil. I would use a good quality  oil and wash it properly

Thanks that all makes sense now that you say it.

[joerobson]

What is the Ground?

[J M Pryor]

Just now, joerobson said:

What is the Ground?

Shellac and water stains

[jezzupe]

is it only doing this under lamp and or sun...bubbles are outgassing/evaporating solvents , a good ground as suggested by Joe will reduce outgassing based on "filling" the "pores" and by disallowing the creating of a "cup" and or pore of solvent that will be prone to evaporating out as the layer of varnish tries to skin over the top.

the surface tension of the varnish will allow it to span over pores to "skin them over"  if there is too much solvent in the mix or if no ground was used the formula can be prone to "outgassing" 

a varnish that was laying flat and then suddenly starts to bubble may be doing so because heat was introduced via sun or lamp, thus creating rapid outgassing that can bubble up as it breaks through the skinned varnish.

Some varnishes need to "sit" on the instrument for awhile until the initial solvents outgass and then lamps can be applied....Many times a freshly varnished piece will bubble if put immediately under lights or in the sun, where as the same piece 6 hours later will be fine under lamp or sun.

[joerobson]

On 8/11/2019 at 8:38 PM, J M Pryor said:

Shellac and water stains

Looks like alcohol bubbling through the varnish. My guess is that it was in the sun. Perhaps moved from an air conditioned shop to outdoors in the sun.

on we go,

Joe

[Nick Allen]

1 hour ago, joerobson said:

Looks like alcohol bubbling through the varnish. My guess is that it was in the sun. Perhaps moved from an air conditioned shop to outdoors in the sun.

on we go,

Joe

I never considered that alcohol needs to gas out that long. How long should one wait after using shellac or spirit varnish before putting anything over it?

[joerobson]

25 minutes ago, Nick Allen said:

I never considered that alcohol needs to gas out that long. How long should one wait after using shellac or spirit varnish before putting anything over it?

At least an hour after the odor is gone...for oil varnishing.

Joe