Friday, June 12, 2015

Review of image transfer techniques using acrylic gel and medium


The web proposes many methods for transferring images to - according to the claims - mostly any type of surface. Owing to what I'm used to work with, I thought the techniques based on acrylic gel were worth a try, for a limited investment (at least in terms of money).

I started from Google and Youtube, to look for tutorials and tips. You can find a big amount of them easily. One of the recurring problems with these tutorials (and the comments that often accompany them), is that you are often confronted to contradictory information (typically: "this works only with laser-printed paper" versus "this works only with inkjet-printed paper").




So I've bought some acrylic gel to see for myself. My first random attempts produced results that were... random. I've tried to refine my tests according to the recommendations of tutorials that seemed better done, but it was still disappointing. So I've decided to go for a little campaign of systematic tests and for taking the time to do it well (and let things dry as needed).



I have defined several alternatives for the technique, based on the tutorials, on some of the previous random tests, and on some ideas and intuitions.

The basic operation is always the same: the image is printed/drawn on a piece of paper, a layer of acrylic gel is deposited on a piece of plasticard with a brush, and the paper is laid on the layer of gel, with its printed face down.

At this stage, there are already two options: apply the piece of paper as it is, or first soak it wet (to facilitate the migration of the pigments according to the claims). So I have divided my samples in "dry" and "wet" categories.

The samples are also printed on different supports: normal paper, tracing paper (papier calque) and plastic transparent (the ones used with the good old overhead - transparents pour rétroprojecteurs). I tried the last one after viewing a tutorial. The idea of using tracing paper is that I expect the pigments to be less deeply fixed in the paper due to its density and its nature a bit more "waterproof" than normal paper.

The "mobility" of the pigments (their ability to get away from the paper fibers) in order to be absorbed by the acrylic gel is an important parameter. According to the contradictory statements found on the web, I've printed some samples with an inkjet, and some others with a laser printer. From some of the previous random tests, I also noticed that graphite from a pencil and indian ink (encre de chine) had some good ability to be transferred. So I also tried samples that actually consisted in drawing over a printed image either with a pencil or with indian ink. In all cases, the samples are left untouched for 24 hours after being printed/drawn over, to let everything dry correctly. This decreases the risk of the pigments spreading randomly due to the moisture during the process, and creating dark halos, ...

All in all, this makes a big number of samples:



Dry paper (A) Wet paper (B)
normal paper + inkjet A1 B1
normal paper + laser A2 B2
normal paper + ink (*) A3 B3
normal paper + pencil (**) A4 B4
transparent plastic + laser A5 (***)
tracing paper + inkjet A6 B6 (****)
tracing paper + pencil A7 B7 (****)
tracing paper + ink A8 B8 (****)
tracing paper + laser A9 B9 (****)

(*) The ink is set above an inkjet-printed image. Small drawings using a Staedtler Pigment Liner were also added to check if that kind of pen works as well.

(**) The pencil is set above an inkjet-printed image.

(***) Transparent plastic is waterproof...

(****) no picture available. It has been tested earlier and the results were not good enough to justify including them in the systematic comparison. However, the conclusions cover their results.



So as mentioned above, for each sample, I cover the plasticard with a layer of acrylic gel, and I lay the paper over it, and let it dry for 24 hours.



First observations about the wet samples:

- when drying, a differential dilatation occurs, inducing significant bending of the sample (both with normal and tracing papers). This bending disappears completely when you remove the paper (actually, it even disappears as soon as you wet the paper again). This is a normal behavior and it can only be avoided if you can find a proper way to apply a pressure while still allowing the sample to get dry. If you're transferring the image on an isolated part, or on something that is very rigid, it will not be a problem. If you envision the transfer on an assembly with flexible elements and weak points, this may be a real problem (cracks...).

 - the tracing paper tends to undergo a significant wrinkling due to the moisture, that does not disappear. If the wrinkle passes through a part of your image, it will not be transferred on the new support.



The cleaning/removing of the paper from the sample depends on the type of paper used:

- normal paper needs to be wetted again, then you peel off what you can (which is not much usually, less than 10%) and you get the rest away by rubbing it away gently (see the video tutorials below for good examples). The cleaning process is long and errors are easy to make (rubbing off too hard).

- tracing paper needs to be wetted too, and then you can peel off most of it (90% or more) in a few pieces. It works much better if you actually guide the water between the tracing paper and the plasticard (for example with a flat brush) to weaken their bonding. Then you just rub away the residuals, in the same fashion as with normal paper, except that it comes much more easily.

- for transparent paper, you just peel it off in one piece and that's it (but you have nothing left actually...).

In the pictures below, I did not always go through the whole cleaning of the samples with normal paper, because it would have been very long. I usually stopped when it seemed that the ink was removed by the cleaning. A more precise account is given below.



Dry paper (A) Wet paper (B)
normal paper + inkjet


normal paper + laser


normal paper + ink (*)


normal paper + pencil (**)


transparent plastic + laser

n/a
tracing paper + inkjet

n/a
tracing paper + pencil

n/a
tracing paper + ink

n/a
tracing paper + laser

n/a

The results are illustrated above. In several cases with normal paper, I didn't go through the whole cleaning process because it was too long, and not necessary for the conclusions:

- contrarily to a video tutorial from Youtube, the transparent plastic + laser didn't work. Maybe the printer parameters I have used were not the good ones, or maybe that particular plastic, and the way it interacts with the laser + toner cannot work with this technique?

- wetting the paper does not seem a good idea all in all, either with normal or tracing paper. The amount of bending is very large and in general the transfer seems more fragile to the cleaning than with dry paper. Even with laser-printed drawings, the result is clearly less good than with dry paper. With tracing paper, the amount of wrinkles induced by the moisture can be a real problem also. So I'd rather not recommend wetting the paper.

- techniques based on dry normal paper work somehow, with very different results:
  •  in the cases of inkjet printer and indian ink, the ink was not actually transferred to the gel, meaning that if you remove all the paper, the drawing goes away with it. So in these cases, the gel acts more like a glue and you have to accept leaving a very thin layer of paper, which means a slightly grainy surface. It is quite likely that this roughness will mostly disappear if you paint over the drawing with acrylic paints. So this may be not too much of a handicap.
  • in the case of pencil, the result is not homogeneous, but it is not bad. Some of the graphite is actually transferred to the layer of gel, and you can then remove all the paper without removing the drawing everywhere; you will have some damage, but the result may very well still be practical if the drawing is not too complicated. Softer pencils seem to be advisable to draw dark lines easily. The dry normal paper + pencil is not the best choice, but gives good results if you cannot implement other solutions.
  • laser-printed paper gave the best results by far. The toner is actually transferred in the gel and you can remove all of the paper without damaging too much the drawing. The result seems a bit better than with the pencil, and it also has the advantage of avoiding the step of having to redraw over the whole drawing before going to the gel step... So dry normal paper + laser printing seems the best choice in terms of quickness and efficiency. But you need to have access to laser printers. Fortunately, typical copy shops use laser printers/copiers, so this is not too much of a problem.
- techniques based on tracing paper give, in general, much better results than techniques based on normal paper (at the exception of the wrinkles when it is wetted). As expected, the pigments are less deeply bonded to tracing paper, due to its higher density and particular structure, than they are to normal paper. On the other hand, the stiffness of the paper does not facilitate the good adherence between the paper and the gel, and is prone to wrinkling even under the sole moisture of the gel (but it is much less severe than when it is wetted). Inkjet gives the poorest results. Indian ink is nice and gives a high contrast, but there is a little risk of halos when the paper is applied on fresh gel. Pencil gives a reasonnably robust result, with some defects that are not a problem on drawings with a moderate complexity. The other advantage of tracing paper, is that you can practically do the whole process without a printer at all. So dry tracing paper seems a better candidate than normal paper, whatever the solution for the drawing laid over it. If the risk of wrinkles is not a problem for your drawing, then I would definitely recommend it. The combination dry tracing paper + laser printer is the quickest and easiest option.

These results may be specific to using plasticard as the new surface. It's very likely that non-waterproof and/or fibrous/porous surfaces behave in a much better way by allowing a stronger bonding of the gel layer and/or by absorbing it totally or partially.



...last-minute test...
During the discussion clerk in the art shop where I bought the acrylic gel, he mentioned that acrylic medium should work as well as acrylic gel. This, combined to a tutorial recommending to use a gel as thin as possible, convinced me to do a last test, with the 2 best candidates of the preceding test campaign.
 
 Left: dry normal paper + laser printer. Right: dry tracing paper + laser printer.

The results are not bad. The tracing paper is less good but it is probably due to the fact that I think I didn't press it hard enough. Or maybe it is due to the fact that this combination has induced large bending deformations, that may have decreased the quality of the bonding. Due to this large bending distortion, I don't recommend this combination.


Updates:

1) I have tried again the combination acrylic medium + laser-printed (dry) normal paper twice, in good conditions. The result was pretty good, even better than above. But you have to make sure that you press firmly the paper on the medium from the beginning. So this definitely seems like a good solution.

2) I have also tried to put the medium on the paper (and not on the plasticard) and then to put the paper on the plasticard; the result was very poor as the medium remained stuck to the paper, and nothing was transferred in the end. I don't have an explanation yet, because only 2 minutes elapsed between the application of the medium and the contacting of everything. It even happened with 3 samples in parallel. Maybe I didn't apply a sufficient pressure?



Conclusion

From these tests, it is difficult to make a clear choice without an application in mind: laser printer definitely takes the lead in terms of easiness and results, but the choice between normal and tracing papers could be discussed.

Techniques based on pencil or indian ink (or pigment liners, etc) are basic, but they can producre very nice results, but they work definitely better with (dry) tracing paper. They are nice if you don't need/want to go through a computerized process, also.


In the particular case of transferring images to a structure made up of plasticard such as the Ice Cream Man truck, I take the following aspects into consideration:

- I will avoid techniques creating large bending distortions, I don't want risking the joints between the panels of my truck to crack due to the bending.

- for the drawings covering large 2D areas and with a high level of details and/or lines difficult to reconstruct if absent, I will rather avoid the tracing paper, because its tendency to wrinkle would be quite risky.

- for drawing covering small surfaces and/or elongated areas, tracing paper may be the best candidate (I expect the risk of wrinkling to grow with the surface of the paper and to increase when the 2 dimensions are comparable in size... something like a Poisson's effect).

So all in all, for the truck, I think I will opt for dry normal paper + laser printer. I'm not sure yet if I will use acrylic medium rather than gel. I will probably do another set of small tests just to make up my mind, and to be better prepared for the real thing. I would also like to find a way to improve the positioning of the drawing on the surface. In these tests I had no constraints. For the truck, it'll be the exact opposite...

Last tip: don't forget to mirror your image before printing it if its orientation is important (presence of text, etc).



P.S.: the HTML code for the tables above was generated using http://www.tablesgenerator.com/html_tables , which I found was a very convenient and powerful tool.

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