"Saline etch" on aluminium - effective resists ?

[ainesse]

Perhaps someone can please help.

I have just started using the saline etch on aluminium process and while it worked and that was exciting, in a way - the opening which occurred to the thin lines I 'scribed" into my oil bar resist coat, really were quite widened during the etching process  resulting in a rather rough looking and jagged line.

Any thoughts comments on what I might try next?

I have attached a jpg of the etched plate so the quality of the lines can be viewed.

thank you

[Nik Semenoff]

I hoped someone else might have a suggestion for your problem, but I guess I will give it a try. Since I don't do intaglio prints and only have done research into processes for the sake of my students, I don't have all that much practical experience as many others. I suppose the oil bar resist is just you spreading the color to produce a film as a resist, but I wonder just how perfect can it be? Do you do anything to make sure you have a thick enough and continuous layer through which the mordant can't break through. Have been using the oil bar resist with acids on other metals? I have found that this mordant can break through Future floor polish, which has been popular as a resist.

In my limited research and experience, I have found that the electro-chemical action of copper sulfate mordant is very similar to electro-etching as they both can find the smallest break in the resist. Acids form hydrogen bubbles that tend to stop the etching action unless brushed off with a feather, while this mordant does not produce large or enough gas to interrupt etching. I would suggest first trying other grounds that are known to be good resists against mordants.

There must be others out there with some experience along this line.

[Graver]

Hi
I've found that the floor polish resist is best when two coats are applied. Let first dry thoroughly then apply second.
Also using vegetable shortening as a lift ground works well for expressive painterly mark making.   
Melt in microwave or hot water paint on plate and when dry pour liquid resist over (2 coats). when dry immerse in hot water to lift the ground away.  As its on aluminium you don't need an aquatint

[Alfons]

I've found that applying a double layer of resist (Future or Klear) can make the ground difficult to draw through.  As an alternative, the acrylic floor shine resist can be improved by adding a small amount of an acrylic medium, such as Golden GAC 200, or an acrylic varnish (Lascaux Transparentlack Gloss).  I add 30 ml of medium to 500 ml Klear - the resist can be coloured too (I use Daler Rowney Artists Acrylic Drawing Ink for this).

I would also recommend allowing the resist to "cure" properly before biting - drying using heat will help too.

An effective lift ground can be made using Art Masking Fluid (or liquid latex rubber glue such as Copydex) coloured with gouache.  If using Copydex, you may need to thin the mix with water.  Lift the resist by placing in a tray of warm water (not boiling!) and by rubbing gently with your fingertips.  The rubber solution is softened by the heat of the water and should lift easily.

[Nik Semenoff]

Alfons:
For some reason my computer does not flag new posts and I miss them unless I check every section in the forum. 

Re your suggestion of using rubber masking fluid as a resist, by purchasing Art Masking fluids in an art store. For many years I have been using a perfect substitute for this expensive material by going to a craft store and getting a thicker material meant for making plaster castings. It is exactly the same rubber emulsion but much thicker, but much cheaper. It might still be available at floor covering stores, who use it to glue rugs together at one time. Just use water with added household ammonia to dilute it to the viscosity you like. This source give you the same product at a small fraction of art store prices.

[nicky]

This may be a year too late!.....I use Graphic Chemical liquid ground and find that it is very effective. There is occasion foul-biting if not applied evenly. Both it and a liquid hard ground from Charbonnel (Lamour black satin hard ground) need to be removed with white spirit or oil. The Charbonnel is three times the price but is absolutely first rate: fine lines remain fine and there is no foul-biting.
I find that the Klear floor polish shatters  if it is unevenly painted; it has to be flow coated.
Cheers Nicky

[pronier]

I made an etching with aluminium, it works fine using saline etch.
Nevertheless I've a concern about. A friend of mine, (Gary Thibeau french printing press builder) does not agree with following comments  we can find in litterature about saline etch:
As with zinc, the Saline Sulfate Etch for aluminum produces of a loose coppery sediment which floats to the surface and needs to be removed regularly. Unlike with zinc, a continuous rising of small hydrogen bubbles (not considered a hazard) also indicates that etching is in progress. 
He wrote on my forum(   http://aquatinte.forumactif.com/forum-aquatinte-f1/    ) this is chemically impossible according to the components:
Copper sulfate, Sodium chlorure, water and aluminium.
Who can give here the chemical reaction formula?
Thanks from France to all of you
jean-claude
PS sorry for my bad english...

[pronier]

Hi
about my previous post and to avoid misunderstanding, the point is not to be in doubt at saline etch quality but to explain hydrogen bubles origin when bitting aluminium.

[Nik Semenoff]

When salt and sodium bisulfate are mixed, they form hydrochloric acid, the strength depending on how saturated the solution was made. Hydrochloric acid attacks both aluminium and zinc with the production of hydrogen gas in all cases. This flushes the fine copper particles from the etched line, but the actual removal of metal is taking place on an electro-chemical level, depending on the potential voltage difference between the metals on the electrical reaction scale as compared to hydrogen. This is explained on my site at the university of Saskatchewan in the paper co-written by Dr. Bader and me. In the meanwhile, the hydrochloric acid is also dissolving a small amount of the metal to form hydrogen and a chloride of that metal. The two reaction have no bearing on one another, only that they produce metal salts the might get into some final reaction between themselves to form solids that will eventual precipitate. The chemists with PHD's told me that the reactions can be very complicated even though it looks simple at first. I have seen attempts on the Internet to explain the chemical process, but it really doesn't come close to what I was told by our chemistry department.

Since I can't remember the valances for the chemicals, I will just give you an indication of what is happening. Al+CuSO4 = Al(SO4)3+3Cu. While this looks like simple chemical reaction, it is the metals voltage difference that removes the aluminium to give us copper. The hydrochloric acid will attack the aluminium: HCl+Al = AlCl3+3H. Along the way in the bath, the salts will react and might even bring water into the process to produce aluminium hydroxide Al(OH)3, when the bath loses its acidity. In the meantime, there will be cupric chloride and copper chloride, depending on acidity and presence of free oxygen in the solution. If cupric chloride is formed, then the bath will regenerate for use again.

There is no reason to filter out the copper particles as they are necessary to regenerate the mordant more quickly. If there is enough salt in solution, it and bisulfate will dissolve the fine copper into sulfate - but more likely chloride. If left in an open tray, solution tend towards cupric chloride that is very effective in etching metal. I suggest you read about the new method I developed of etching copper with copper sulfate by converting it into cupric chloride. It is on the home page of this blogsite. Also on how to eliminate all toxic chemical from the spent mordant before pouring it down the drain.

By the way, I prefer to call it salt etch as that was the name we gave it at the university when I developed it in 1992.

[pronier]

Many thanks Nick.