exposure times with the sun

[gozo]

After my complete failure with a vinyl stencil, I am planning to use sericols dirasol 916.
As at the moment I do not have any exposure unit, so since we have quite a few sunny days I will try to expose my stencils via the sun.
My question would be with the UV factor being 3 how many minutes would I need to expose the screen.
BTW I will be using dark vinyl as a stencil for the exposure.

[mono_666]

Im not sure what you mean by "uv factor being 3"... but I live in california, I use 925wr, rubylith, and a sheet of glass... takes me 45 seconds to burn a screen... also I only burn when I can see defined shadows... not sure if that matters, but Ive had failure on gloomy days

Depending on emulsion, and how bright it is, I would just experiment... youll waste afew screens, but then youll know.

BTW, where do you live?

[gozo]

I live on an island in the Med. the 3 UV factor for the day I just got from my local newspaper. Today has been a cloudless sunny day. Thanks for the advise.

[James flames]

I use the sun all the time. Takes no more than 45 seconds on a bright sunny day, about 55 seconds to a minute on a slightly cloudy day. Like Mono says, as long as you see shadows, you're good - though I'll tell you I've burned a screen with cloudy skies and a slight drizzle, and it still worked really great (it was around 12noon). It took about 2.5 minutes, but it was a totally crisp burn for sure.

[oldbox]

why the sun maan....
two of these and a glass plate 2 min max

[El Roacho]

because those are just little suns, the big one is free.

[gozo]

Hi old box, I,m doing it on the roof because I have no space in the apartment, I have the sun, and I have a nagging wife that is a pain in the arse.

[Brad]

what is this thing you guys call sun?

[vrooooom]

The UV factor is calculated by combining and averaging a number of uv readings. It's pretty much worthless for calculating an exact exposure, because there's a particular bandwidth of uv that will cure your stencil.

The sun is awesome, but it can also be frustrating. I think with a vinyl stencil, you'll be pretty well off. Pretty opaque I'm guessing.

But you need to run exposure tests to get in the ballpark. We don't know your coating technique, mesh count, mesh color, blah blah blah.

I've done screens from 1 minute in sun at noon to 30 minutes on an overcast day. Dual cure, ulano lx-660. Vellum positives, yuck.

Grab a stouffer scale?

[gozo]

Afraid i can't get a stouffler as the supplier does not have them.
However my mesh is white 90T and I will be using sericol dual cure emulsion dirasol supercoat 916.