Exposure times

[AJLA]

There will probably be a looong list of questions here over the next weeks as we prepare to begin using our screen printing equipment so here's just the start:-


We have a 500w (cheapo) halogen lamp.. what would be the expected exposure time for this wattage or should we increase it?

Also at what distance do you position the lamp from the doofer (minds gone comletely blank!!)

[John G]

Hi, It all depends on the emulsion used as they often have different timings and a variety of other things such as distance between glass and bulb, strength of bulbs, freshness off emulsion, how the screen was coated, how many coats per side etc etc.

I'm using fotecoat 1072 (Colenso) coated once either side - distance from bulbs around 65cm and its cooked for around 4.5 to 5 minutes (old bulbs).

Its all trail and error, years ago you used to be able to get a posi guide from whoever supplies your emulsion but I haven't seen one for ages. Just give it a go - if the emulsion breaks up and washes off completely you need more time - if its difficult to wash off, or doesn't wash off at all, you need less time - this is with a power hose which you will need. Don't blast it with full power though :D or too close.

Cheers John

[AJLA]

Oh thanks John G ..I was hoping you would be around. :D

So trial and error, and probably lots of it it just seems it's going to be a lot more difficult than sublimation, just what you get used to I suppose.

Interesting tip re wether the emulsion breaks/washes off completely or not. Now how the heck would I have known that :shock:

Perhaps we should start off at 4 mins? As we don't know how old the bulb is, perhaps I should even get the paint first :lol: Which we will be ordering next week and leads me to my next question do you have a variety of colours in stock as we do with vinyl or do you mix them up against some sort of colour chart? (don't like the sound of that at all)
Thanks John.

Back in a minute with more mind so don't go too far hey :lol: :lol:

[John G]

I stock a range of inks and mix by eye using rubbings to attain whether you need to add certain colours. You can mix using scales and set ratios/weights but I was taught to use my own judgement when I served my time. After a while you do see the colours and know instictively which colours to add and how much.

At first buy the colours you'll need for basic t'shirt printing - black, white, red, blue, yellow would be a good start. Adding to this over time with the likes of magenta, kelly green or a few of the other obscure colours - you'll soon get the hang of it.

Don't forget you'll need plastisols for fabric, nylobag or similar for nylon, and polyplast or similar for vinyl/sticker work.
A pantone book also comes in handy along with colour charts from your ink suppliers.

Have fun :D

[AJLA]

:shock: :shock: FUN you say well I was looking forward to my new beginings but now i'm not so sure.
Not really looking forward to the mixing stage (we're a loong way from that luckily) but as you say it takes time and judgement which is exactly what I do now with other printing methods with my eyes closed and without a second thought. But I was wondering, if you mix a batch up for someone (using your own judgement) and six months later they are back for another, how do you get exactly the same?
Is this where you will have had to mix using scales?

So we will start off with Plastisols in the popular colours, a lot of our own work is just white text on black shirts, is there anything in particular I should source?

[John G]

If mixing a particular colour for a job you know won't be repeated just mix enough for the job. If you think there may be a chance of using the same colour again mix a bit more to keep in stock. At first keep a notebook of the colours used for each mix as a reference for next time - as in: 1 scoop blue, 2 scoops yellow etc.

If you printing white onto black you may need a flash dryer.

Cheers John

[AJLA]

We have a flash dryer so thats a good start.

[AJLA]

We have made our first screen up John as you suggested, with various text sizes. The timing fom 3 mins up to 20 in stages. It appears that between 9-11 mins seems to be better. The end closer to the 20 mins time was much more difficult to wash than the 3 min time where it almost washed away. We also found that the stencil in black vinyl which we would have pressed onto a shirt was better than our possie.
We are going to do another trial tomorrow and also order some more screens to start our collection.

[John G]

Yes, cut vinyl can be used for a posi - anything that won't let light through. Now you have your timings its all systems go! :D

Cheers John