Knowing about how screen printing worked when twisted multi-fiber thread mesh was common or the only thread available and synthetic threads were new is interesting but new products only hold a basic similarity in performance to that primitive equipment.

A laundry mangle is an interesting tool but knowing how to use one has noting to do with current methods for home clothing washing - compare that to what we have now in screen printing. Talking about chromate emulsions or rope and groove screens has simply become inapplicable history. Anything from the industry 10 or longer years ago is only interesting reference, mesh alone has improved vastly and even retensionable screens have had wonderful changes and additions in the recent years.

I started screen printing many years ago trying to find a way to make airbrushing t-shirt designs faster, I never stopped even when I wanted a "real" job. Of course how long you have been doing something, often wrong, and that would include myself, is not as important as if you listen, communicate and search for new information, you could call that continuous improvement if you like - see it fix it!

If a product works, why live with something that is as harsh on you as carburetor cleaner? Surely some harsher chemicals work faster or even "better" and I present this issue in every class. In fact, in my class we use examples of the mildest soy based chemicals, organic extract based chemicals, and the harshest of petroleum chemicals side by side so the students can see exactly how they work and make the judgement for themselves.

Lots of small shops start off in a building in a retail location with neighbors, and some (where legal) even start in their basement or garage - odor and close neighbors can be a big issue in this industry. I try and help the students understand efficiency in lots of areas, including art, exposure, reclaiming, and where some new products can even eliminate or shorten some steps. Certainly many things are not for every shop, but I like to review as much as is needed. Because I specialize in helping new and small shops I have learned you have to have some mercy and lots of patience.

I even have several sections in my class presentation where I talk about alternative products, how they work, and products that have real equivalents OTC (over the counter) and things that are simply myths or frustrations waiting to happen. In fact we are on the 20th revision of the class with a new workbook filled with custom drawings, micro photos, and information provided by the people who know, study and make the products.

Its not information just to fill pages, our class is filled with facts we have gathered continuously for years. We make continuous changes to the class when new products come out, and new methods emerge. We always look for the next screen printing myth to test - if things change or new facts come up it is immediately in the next class. I have found that if you want to know about emulsion spend time asking the great folk in the labs at the manufacturers factory. If we want to know about inks call a trusted representative then get a sample - find out - and try it out.

On a final note we don't compete with our customers, or students. We are in the industry to educate, and my part is to study screen printing, observe, test products, and work directly on site with shops providing information and troubleshooting. I am not going to manage the day to day operations of a business that would be competition with our students, many who end up as great friends.

I have been criticized for my use of a microscope in the industry, but what is nice about a tool like a microscope is that you can show why things like EOM work and why printed dots that are very small don't print well on t-shirts. A microscope will show how small dots can drop into a thread crevasse. I have found that the microscope gets lots of "ah-ha" moments especially with printers who have done things in an outdated way or with outdated equipment or methods, it shows clearly the limitations with equipment or product and points out the function and limitations of the five basic types of emulsions. In other words it is a great educational tool I like it and will continue to use it to help our students.

A subject that is coming to the forefront more than ever before.

I crosses several subjects and i starting to become something that I know is very workable in some situations.

I started in several places and with several parts but is just now coming together for several shops in a very profitable way.

Here is where it started.

Small shop of one person and limited occasional help, moves to a new location where wash development and reclaiming screens is an issue, reclaiming screens is almost impossible because of a new private sewage system.

The first answer this shop had was simple, just don't reclaim and tank the development water to be processed off sight by a public/commercial sewage collection service. This shop was collecting more than enough in charges to cover a new screen for each color - the answer was to buy screens, coat, and expose, then print and after use an on-press wash and set the screen off to the side to be discarded later. This presented a small storage issue, but a huge gain in production time available - zero time reclaiming screens. The screens are heavy and shipping was an issue. Of course I flinch at the thought of a screen "trash canned" like that and tried to convince the shop to at least sell them on e-bey, that failed, they did not want the designs to go to other shops (fair enough).

Final answer we worked out involves several steps and would not be a great fit for every shop but once all the cost and profit were reviewed with the gains in hours used for production rather than reclaim the results were dramatic. This is in action in several small shops currently.

Here is how the procedure works.

Base retensionable screens with table, three days of production.
Insert panels of mesh.
Degreasing chemical and/or chemical stain remover.
Capillary film preparation chemical.
Capillary film.
Quality positives for full exposure and lowest time and water use in wash development.
Current Manual printing equipment.
On-Press Wash of customer preference.

Shop did choose to use a hybrid frame and table with mesh panels, the needed mesh is chosen and locked onto the frame and brought to full tension.

Mesh is prepared for wet application of cap film by first an application of a mild stain remover and short pressure wash (less water use), mesh is then sprayed with a cap film preparation chemical and the necessary choice in cap film applied using the wed roll-on method (this saves a dry step).

Once the screen has the cap film applied it is dried in a high airflow drying cabinet and then exposed, washout is with a light mist and then high pressure wash out with a pressure washer in fan spray, this is where a quality positive lower water use.

Screen is dried then blocked out, dried, (often the block out is skipped) taped with a screen tape and used for printing.

Once the job is printed, rather than reclaim the screen the ink is dry-wiped then a mild on-press wash is used and the panel is removed with the screen table, the frame is placed in storage for the next use.

The snap in panels are a quick ship, light weight item that has a total cost lower than shipping heavy frames each job, possibly they could be sold or even reclaimed later if needed.

At first I thought the idea was heretical and insane until I reviewed the profits captured, efficiency wins, it's not for every shop but it does work, very well in the correct application.

So is it screen printing heresy? or in the right situation just good profitable business?

Recently there have been several machines capable of applying ink, wax, or other media directly onto a screen's layer of emulsion to replace the positive. Basically everything we need from the positive without the film. More on this later.

Without waxing poetic about the past or pontificating too much lets look at the issue of positives, RIP software, and exposure.

Back many years ago when many of us were foolish enough to think that we could get away with "laser printer" positives, we tried to replace our far superior silver/chemical based film positives. Our camera shots, even the PMT shots had both darker "blacks" (a higher D-Max) and a clearer base film (D-Min) than vellum or the frosted film. We thought that we were saving time and money by shooting toner based positives quickly from a laser printer, we sprayed them with a repackaged artist-fixitive (something that always worked better than hair spray - it was the evaporative solvents that did the "melting" of the toner) and passing the quickly printed vellum to the screen room.

Of course this only cost the "screen room" time and effort - far more than we were saving in the "art room" we were soon forced to shoot paper positives with the old manual cameras to make reasonable positives. This did not last long, and as soon as we were able to justify to the ownership we needed an image-setter, life was good. We had more time for more artists to print more product. Production with excellent positives shot to the roof, and that was when a Harliquin RIP and a VLR image setter with chemical developer was a 48K investment.

In the industry there has always been the old argument over what was more important D-Min or D-Max. the REAL issue is CONTRAST it is not just the clear of the film or just the dark black but BOTH. We want the best of both, simply better is better, high quality always trumps mediocrity.

Discounting the need for a good D-max is showing a basic misunderstanding of how electromagnetic energy or "Light" works and how emulsion is exposed. Light waves never "slow down" - light is light and it either is blocked, bent, (refraction), or filtered. Light continues on - always the same speed - the speed of light. Reaction times change in emulsions based on the volume of light energy.

The lower the D-Max the less light is blocked (more accurately filtered) and the more electromagnetic energy passes through the dark areas. The dark areas of the positive control how much light is filtered, the lower the density/opacity the more light will pass through into the emulsion layer. Regardless of how powerful or fast the exposure the light always is the same speed and any light that passes into the dark areas of the positive and is not filtered continues on to the emulsion and starts the exposure reactions in the emulsion.

Here is an example of a poor black on a positive, even with a ridiculously thin coating of emulsion to compensate by shortening the exposure - it clearly did not work. A correct and full exposure has this and other negative results with a poor positive.

It is always in the facts, the microscope tells all, poor positive, poor results or you are forced to underexpose.

What does this have to do with a RIP?

Inkjet printers without a RIP in front will only deposit a particular pre-determined amount of ink on each dot from the piezo head, this is measured in picoliters (One millionth of a microlitre; 10-12 liters) a very small amount of ink, and that is always set at about 3 to 4 with the free software for the printer.

Epson printers have this setting infinitely variable via the information sent by the printer driver, in other words Epson left their inkjet printers open to performance modification by software.

To modify the inkjet ink deposit you have to have software that will change the ink deposit. The free driver supplied by the manufacturer is designed for ink deposit to give pleasing or accurate color and will be limited in ink deposit volume to about 4 picoliters per dot including the black inks.

With a RIP the printer is "told" to "squirt" enough ink to fulfill the demands of the user, and the RIP makes this much easier to adjust often with settings from 6 picoliters to 27 picoliters or more per machine dot printed - that is each machine printed dot not the formed "dots" you would adjust as "LPI/frequentcy" in your vector or raster program. Contrary to assumptions a RIP not only converts the image but tells the printer EXACTLY WHERE (so it holds registration) to put a dot and HOW MUCH INK to deposit.

With a thin, poor black as the dark areas (D-Max) the black becomes like the darker areas of an exposure calculator - not dark enough to block or filter all of the light energy and some of the emulsion is exposed behind the black, the more full and complete the exposure the more the open areas under the black are exposed leaving remnants after wash development and forcing the user to "blast" the open areas excessively leaving ragged edges.

With the poor covering of ink from the standard driver you do not create a black that will block sufficient light to keep the emulsion from forming a skin of slightly exposed emulsion over the face side UNDER THE BLACK. To then open the stencil we would have to put enough pressure on the open areas in wash development to "break" the edges of this "skin" off and that will result in an edge that is rough and will present a less than desirable printing "gasket edge" against the product.

Professionals use professional tools, using a RIP has other advantages, the biggest one in art production is using the graphic tools we have correctly. No real graphics professional wants to go back to breaking jobs up and fidgeting with photoshop to get dots or separations, directions for this procedure you can find on the internet for free, but the results are a poor D-Max and the resulting problems.

Postscript a beautiful thing, no serious artist is going to go back to the days before the introduction of Adobe separator (a program that is now imbedded inside of Illustrator and has been for over a decade).

Not using good quality film, quality inks, and a good adjustable RIP, a printer cannot get the real and required contrast from D-Min to D-Max to get positives that will allow professional results with full and complete exposure. The combination of special film for positives, ink designed for positives, and an adjustable RIP are the tripod of good positives with an inexpensive inkjet.

How to START to chose a line count (frequency) correctly for your mesh

There are simple answers and propeller head math junkie answers.

Unless I am mistaken you can find a rather complicated formula for finding exact (yet theoretical) size to mesh relationship.

I tell new people that they can start at 5.5 factors.

230 divided by 5.5 - 41.81 - I start with 42 most of the time.
305 divided by 5.5 - 55.45 - I start with 52

Reverse also - I have to have this broken into dots that are 36 LPI (frequency) so...

36 multiplied by 5.5 - giving 198 so to get the maximum theoretical ink volume (highest opacity by thickest deposit of ink) I can use a 196 to 200 mesh.

This is ONLY a SIMPLE starting point - for advanced users you have to consider emulsion choice (and it's ability to hold detail and bridge well), EOM and your particular mesh.

The best way is to start with a simple and easy idea and build on that with testing.

You can make positive strips with halftones of various LPI on each strip, shoot for your full and correct exposure and develop and print the various sizes with both dark ink on light backgrounds and white ink on dark background and save the results for your art development and choices for mesh and available detail.

First, Stochastic is a bit of a play on words from the Greek into english - to aim, and to guess...

Basically to aim for a "general" result knowing that the end result will be slightly random and unpredictable.

1. Is a stochastic separation virtually the same as diffusion dither?

Almost, but even using first order stochastic dots with a good RIP there are better formations of dots.

Advanced RIP output often works by exchanging fixed grid square dots in a semi-random pattern for round dots semi-randomly placed in a similar fixed grid.

First order stochastic dots are considered primitive and problematic because of the secondary pattern.

The secondary pattern you see here in the red square...

Luckily for screen printers, using stochastic dots is FAR more forgiving of printing with mesh than with other transfer method printing procedures like offset printing.

2. What is the advantage of stochastic separations versus conventional elipitical dots?

On that, how about a bit on what is a conventional or stochastic halftone. Regardless of type "halftone dots" are an optical illusion, where the color is broken into small printable areas to create the illusion of "grey value" or lighter tints of the same color.

Conventional halftones are referred to as amplitude modulation or AM screening. This is an example...

Stochastic dots are known as frequency modulation or FM screening. This example is the more primitive "first order" stochastic screening, an example of the typical "diffusion dither" type.

The good and the bad...

Good--------------

a. Less chance of moire pattern

b. Less chance of frequency interference (moire type pattern on the screen caused by mesh pattern and the dots even before printing)

c. Less chance of moire type pattern forming from the weave of the garment and the dots printed

d. More forgiving in registration

e. More consistent in tone for longer into the print run

Bad--------------

a. Soft focus look (sometimes not a bad thing, like babies, women, flowers and nature prints)

b. Grain like visual effect to open and mid tone areas

c. Dot gain compensation is more difficult

d. Advanced Second Order, combination, and hybrid stochastic dots require expensive sophisticated RIP software

3. Some basic playing around appeared to have the stochastic seps spool/print much faster than the conventional. True?

If you mean that printing diffusion dither conversions from photoshop is faster - yes, the files are much smaller and take the RIP far less time to image because photoshop has already dictated the print placement. Stochastic screening generated from a RIP especially second order or hybrid takes longer to process because of the complex load on the RIP.

This is first and second order stochastic - first order is more primitive and second order is more random with random placement and random dots.

There are two forms of second order the first was random round dots outside of the typical grid and then, more advanced dots of random size AND random non-grid placement.

First order stochastic...

Second order advanced stochastic dots...

4. An article I found has me creating a layer for each chanel, converting to greyscale, then outputting as a bitmap at 150 with diffusion dither. Is this correct, or is there a better way?

You can adjust the dot formation DPI grid, but to form stochastic of the first order without a RIP programed to make stochastic you have to form them in photoshop as described above. You can also set photoshop to use patterns you pick, so you can play with the results, some will be horrid and some cool...

There is also a new hybrid screening technology where the dots change on the same positive from AM to FM screening and back, this is considered the most advanced technology. Hybrid technology uses each type of screening for its strongest features in the most advantageous positions.

Also many printers use a combination technique, where the yellow screen in four color process is stochastic and the other colors are AM screening - this allows the use of three of your best angles and discarding your worst performing angle of the four...

Other types of printing, like offset are working hard on this technology in a desperate attempt to gain an edge with image printing on flat goods like paper publishing. "Art publishing" where image of the print is the reason for the final consumer purchase, has been working with stochastic for many many years...

The first attempts at random pattern stochastic dots were with separations painstakingly sprayed by a skilled separation artist with an airbrush - long before computers!!!