Temp and uv curing box

[saintjohnbarleycorn]

I have my curing box in a space that will go down to about 20 f tonight is that ok or should I move it to a warmer room

[JacksonMaberry]

That seems a little chilly. The relationship between temp and humidity is the most important factor, I'd say. If possible, try to keep the inside of the box from going below 35% or so RH.

[joerobson]

1 hour ago, saintjohnbarleycorn said:

I have my curing box in a space that will go down to about 20 f tonight is that ok or should I move it to a warmer room

My shop is that way too.  I don't find it significant.  Actually some varnishes like the cold...especially cold sun.

Joe

[donbarzino]

If you have lights on inside the box, I think it wouldn't get that cold in there.

You could add some insulation to keep the heat in there, even a blanket would help.

[Jim Bress]

As temperature goes down the RH will increase, but you still need to measure to know what your RH is. If the room is already a bit dry then the warmer environment in the UV box might make for a too dry environment. Or maybe your space is a bit damp, then the UV box will be moving the RH in the right direction. You won’t know until you test. 

[Bill Yacey]

Heat isn't what causes the varnish to polymerize; it's the UV light. You can get a sunburn in the Canadian arctic just as easily as on the beaches of Florida.

[Evan Smith]

I use a repurposed refrigerator with a fan, and adjustable light bulb for heat, I'mm good to go at 20 below.

[JacksonMaberry]

I wouldn't say temperature is insignificant, though it's not the primary driver in curing drying oil-bearing films. That would be polymerization, driven by oxidation. The humidity concern has more to do with the health of the wooden instrument and it's glue joints, rather than the curing of the oil.

From page 264 of Livache/McIntosh.

[Evan Smith]

Yes it dries much faster with a little warmth.

[duane88]

During my years in Salt Lake City, drying oil based varnishes outside in the snow on a sunny day was no problem.

[JacksonMaberry]

Just now, duane88 said:

During my years in Salt Lake City, drying oil based varnishes outside in the snow on a sunny day was no problem.

Outside in the winter is no doubt pretty good. Plenty of oxygen, reasonable humidity, presence of UV. 

[Andreas Preuss]

On 2/6/2022 at 5:36 AM, joerobson said:

My shop is that way too.  I don't find it significant.  Actually some varnishes like the cold...especially cold sun.

Joe

What about humidity?

Isn’t it that some varnishes solidify better in humid conditions? Or if you were to make a Venetian copy you need high humidity for the typical cracquelure?

(I’d be curious to do at least once in my lifetime a violin with Japanese lacquer which must be hardened in very humid conditions.)

[joerobson]

On 2/6/2022 at 6:44 PM, Andreas Preuss said:

What about humidity?

Isn’t it that some varnishes solidify better in humid conditions? Or if you were to make a Venetian copy you need high humidity for the typical cracquelure?

(I’d be curious to do at least once in my lifetime a violin with Japanese lacquer which must be hardened in very humid conditions.)

Andreas,

True.  Some varnishes cure through better in humid atmospheres...slower solvent evaporation helps to avoid top down drying.

As far as cracquelure (an adhesion failure) the jury is still out on that one.

Urishi...I have read a lot but not yet tried it.

on we go

Joe

[Davide Sora]

7 hours ago, joerobson said:

As far as cracquelure (an adhesion failure) the jury is still out on that one.

I believe that craquelure is a problem of internal varnish tensions, not an adhesion problem. Unless you mean a type of craquelures that are so drastic that the paint will lift and peel off, which I personally have never seen.

[joerobson]

I don't understand what you mean by internal varnish tensions.

Thanks.

Joe

[Davide Sora]

2 hours ago, joerobson said:

I don't understand what you mean by internal varnish tensions.

Thanks.

Joe

An underlying layer that shrinks at a higher rate than an overlying one.

[joerobson]

Warmth does facilitate the uptake of oxygen.  However excessive heat is not necessary.

[joerobson]

5 hours ago, Davide Sora said:

An underlying layer that shrinks at a higher rate than an overlying one.

I'm thinking it is time for a thread on craquelure!

More soon.

on we go,

Joe