Wash out issue

[Pantrybarn]

Hey guys. I'm having an issue with the washing out of my screens - in the last four screens I have burned, after they dry from the washing out, there are spots with very thin emulsion, ruining the print. They can't be seen while washing out. The rest of my process is exactly the same as it has always been... The one common factor is the batch of emulsion. Every screen I've done with this batch is having the problem. I just bought a new batch and will try it tonight... but is there anything you can think of that would cause this problem? Thanks in advance guys

[milesstegall]

A. underexposing or B. emulsion has gone bad.. let us know how the new stuff works out.

[vrooooom]

My guess is A, but since you say nothing has changed, maybe something else is going on. Is your lamp old and possibly losing its UV output? Hmmm...

[paul204]

Could be overspray from other screens you were washing out. A mixture of emulsion/reclaimer spraying onto cleaned screens will dry to an emlusion coloured, impossible-to-get-out spot on screens.

If it's a very thin layer, a thorough de-hazing will often help. If it's a substantial amount of emulsion you may be fucked.

[Work Of The Devil]

wash the crap out of them.

[boatdreams]

My guess is that you're not washing out long enough. Be very thorough with the washout. Are you putting them in front of a fan to expedite drying after they're exposed and washed out?
I've had this problem before, and both of those things worked.

[squeegeethree]

There are some threads on this subject already. We call these thin emulsion spots "snail trails". They are usually caused from not developing the screen completely. Remember that you need to develop the whole screen, non image areas included. Spent most of your time washing the squeegee side as this always has the most unexposed emulsion on it.

[Pantrybarn]

yes! snail trails accurately describe what I'm dealing with. by developing do you mean exposing the screen to light? and if i wash the squeegee side won't the unexposed emulsion just wash out?

[vrooooom]

I think squeegeethree is talking about your washout. So after exposing, wash everything and all areas of the screen. If squeegee side emulsion washes out, you're not exposing with enough power to expose all the way through. Think about a steak that charred on one side and still rare inside. Later on, this unwashed, underexposed emulsion, drips down and drys in to impenetrable mess, because it only goes through the whole resistance to water/hardening step once after exposed.

Ulano has a pretty crazy video on screen process, but it's got some good tips and ideas on screen making.

[Andymac]

yes! snail trails accurately describe what I'm dealing with. by developing do you mean exposing the screen to light? and if i wash the squeegee side won't the unexposed emulsion just wash out?

the best check of complete exposure is after washout (and wash the whole fucking screen, not just the image, this is a major cause of scumming/snail trails) After washout, rub your hand on the wet surface. If it is sticky/slimey and emulsion colour comes off, then you are underexposed, or you didn't wash long enough. A properly exposed screen can be washed forever without damaging the stencil.

If nothing comes off and the surface is hard, then your exposure is good.

A good exposure is long enough to 'cook the meat' all the way through, without losing detail.

A good analogy Vrooom, but it would be more like cooking the steak on one side only. the side to the light hardens first, the second side only hardens once the light penetrates all the way through. If your coating is shitty and lumpy and too thick, parts wont expose, and will give off 'snail trails.' And if you only wash the image, that's like cooking the steak in the center, and leaving the outer bits raw.

I'm not sure how that works if you are using vegistencil.