Platinum Printmaking - Chapter 4

Tools of the Trade

Preparing to make a platinum print requires just three basic items—the printing substrate (usually heavy paper) that supports the printed image, the light sensitive coating solution from which the image is formed, and the instruments used to mix the coating and apply it to the substrate. Bostick & Sullivan, a leading alternative process supplier, has put most of these items together in kit form and can provide the rest, as well as invaluable advice. Since I have been doing this for a while, I have also accumulated a number of "extra" tools that make my life easier and/or improve the quality of my work, but none is required to get started. If you contact Bostick & Sullivan, they'll be more than happy to set you up with a platinum kit, high quality paper, and a coating rod and brush for less than US$200. That's what I used to make my first platinum prints, so it's a perfectly serviceable package, won't break the bank, and will give you enough of everything to make around 25 4x5 prints.

Printing Substrate

Every time I've worked on this section, I'm tempted to change "substrate" to "paper," because printing on paper is the most common use of the platinum process, and photographers usually think in terms of paper based prints. However, the platinum process can use any substrate material that will adhere to the coating without causing adverse chemical reactions and stand up to long soaks in water. I have seen platinum prints made on silk cloth and treated plastics, and I'm sure someone will eventually try to make platinum prints on almost anything imaginable—such is the way of the alternative printer.

That said, I print on paper; Crane Crest Natural White Wove, to be specific. It is a heavy, off-white cover stock that is also sold by Bostick & Sullivan as their "Platinotype" paper. Platinotype accepts the platinum coating well, doesn't interfere with the image-forming process, holds up in water, and finishes nicely. I also like the fact that it doesn't yield stark white highlights (unlike most commercial enlarging paper) and pleasantly compliments my images. I'd start with Platinotype, since it's a known and very user-friendly entity, but feel free to experiment with whatever strikes your fancy after you've made a few decent prints and have the process down.

I purchase Platinotype in reams of 23-inch by 29-inch sheets and cut it down with a mat cutter to meet my needs. My standard format is 11½-inches by 14½-inches (four cut down sheets from one large sheet) for 8x10 prints. This leaves a nice, wide border around the printed image, so I have plenty of room for coating and enough space to mount finished prints with archival corners. I use a Logan 650 mat cutter to ensure straight, square, clean edges and can cut down four or five large sheets at a time.

Coating Materials

The Bostick & Sullivan "everything" kit includes two bottles of metal salt solutions (one platinum and the other palladium) and two of sensitizer solutions (one plain and one with a restrainer added). A combination of the four solutions—or at least one metal salt and one sensitizer—makes up the coating solution. In simple terms, the sensitizer is struck by UV light and reacts with the metal salt to precipitate pure metal onto the substrate. The precipitated metal forms the image, and whatever components of the coating are left over are then washed away when the print is processed after exposure.

In my printing, I mainly use the palladium salt, with a little platinum thrown in for good measure. That combination gives me a warm toned image with a contrast range that suits most of my negatives, and because palladium costs less than platinum, it saves money to boot. But just because palladium is less expensive than platinum, that doesn't make it any less capable in other areas. Both are noble metals, which means they are essentially non-reactive and permanent once the metal salt is reduced. Both also look almost identical in a finished print, except that palladium generally prints "warmer" than platinum. In other words, platinum generally prints bluish blacks, while palladium tends toward reddish blacks. However, changes in processing can make platinum warmer and palladium cooler toned.

Platinum and palladium salt solutions should be stored in airtight glass containers at room temperature. They aren't light sensitive, but I still use brown glass bottles, more because that's what I have on hand than any other reason. Platinum is particularly prone to precipitating out of solution, especially if it is stored below 70°F, but it can be re-dissolved by gently heating the bottle in a warm water bath and agitating the solution. Both metal salt solutions have an indefinite shelf life.

The sensitizer solutions are the workhorses of platinum printing. When a sensitizer molecule is "whacked" by UV light, it passes along the punch to precipitate the metal from the metal salt solution. The sensitizer (along with the developer, which completes the reaction) essentially makes the metal image from light. Ferric oxalate, an iron compound, dissolved in water is the sensitizer solution most widely used in platinum printing. It is generally mixed in two "flavors"—one that is just ferric oxalate and water and one that has a chemical restrainer (most commonly, potassium chlorate) added to the basic solution. The purpose of the restrainer is to slow the exposure process and thereby increase print contrast. However, large amounts of restrainer can also lead to excessive graininess in the finished print.

Mixing one standard base sensitizer solution and one standard restrained solution gives very fine control of contrast over a wide range of contrast values. This allows the printer to fine-tune the print to the negative or even use a negative not specifically produced for platinum printing (a "thin" negative optimized for silver printing, for example).

Being light sensitive, the ferric oxalate solutions should be stored in brown bottles, and they do degrade over time. Cold storage doesn't appreciably extend their shelf lives and may even cause the ferric oxalate to precipitate out of solution. Old ferric oxalate will yield prints with more grain and less contrast and shouldn't be used for anything important after about six months to a year. But on the bright side, the ferric oxalate solutions are inexpensive, so it pays to keep fresh solutions on hand, compared to wasting expensive metals.

Coating Tools

To lay the coating down on the substrate, you'll need a coating rod and/or brush. I use both. A coating rod is a piece of small diameter glass tubing with a handle attached to its side. The coating rod is placed near one edge of the substrate, a bead of the coating solution is placed next to the rod, and the rod is used to pull a film of the coating across the substrate. Even though you are actually pulling the coating, rather than pushing it, a coating rod is also known as a "puddle pusher." I like using a coating rod because it gives me more even and faster coverage than a brush.

For brush coating or cleaning up after rod coating, I recommend a Japanese hake brush, but just about any wide, soft-bristled brush will work. I have been told that a brush with a metal ferrule (the part where the bristles are attached to the handle) will contaminate the coating and that it won't. To be on the safe side, I avoid brushes incorporating metal components and use hake brushes with sewn-in bristles. As a bonus, hake brushes can be found locally in almost any art or crafts shop, and they are inexpensive. I prefer the two-inch size, but they are made anywhere from less than one inch across to over six inches wide, giving you have a range of options to choose between.

Pretty much everyone has used a paintbrush at one time or another, so most folks (me included) start out coating with a brush. Brushes are easy to use, give good results with minimal practice, and leave interesting brush marks at the coating's edge. They also waste more coating materials, are prone to losing bristles, and can abrade the substrate's surface, leaving an uneven coating. Coating rods, on the other hand, are more expensive and fragile, and they aren't as intuitive to use. On the plus side, they waste substantially less coating, run less risk of abrading the substrate, and coat more evenly. I usually coat with a rod and clean up excess coating with a brush.

Along with a coating brush and/or rod, you'll also need a very flat, very smooth surface on which to coat the substrate. This is particularly important when using a coating rod, because the rod can't follow an uneven surface, and it may cause surface imperfections to "telegraph" through the substrate. I use a 24-inch by 24-inch piece of 3/8-inch glass as a base for most of my coating work. Before each use, I thoroughly clean the glass, as even a stray hair or speck of dirt can show through the substrate under the coating rod's concentrated pressure.

Mixing the Coating

The coating components in Bostick & Sullivan's kit come premixed in brown dropper bottles, so mixing the coating chemistry for one or more prints is fairly easy. All you have to do is count the number of drops of each component to get the ratios correct. But first, a couple of words of warning are in order. None of the coating components is benign. Each carries its own health risk(s), but with reasonable care—wash hands; don't eat, drink, or smoke while coating; keep coating materials away from food, children, and pets—you should be safe from accidentally ingesting them. None of these chemicals is going to kill you right away, but their effects can accumulate over time, and you should have as little physical contact with them as reasonably possible.

The plastic droppers included with the kit are perfect for the job of measuring small quantities of the coating materials. In fact, "nicer" glass droppers will not give accurate, consistent drop sizes, and they should not be used. One thing that's not included in the kit is a mixing container, but that's easily and inexpensively remedied. All you need is a small shot glass or a plastic medicine dispensing cup (the type that's found on the top of cough medicine bottles). Pyrex shot glasses can be found among the measuring cups in most kitchen stores, if you don't already have one at home. But again, whatever you use, keep it in your platinum kit and don't return it to general household use.

Because I usually coat large quantities of paper at one sitting (30 or more sheets for 8x10 prints), I have foregone the drop counting method and use graduated pipettes. While a single print may only require a fraction of a milliliter of each component (easy to count out by drops—about 15 drops equals one milliliter, and it takes a couple of milliliters of solution to make one rod coated 8x10 print), I generally mix 50 milliliters or more of coating solution at once (that's around 750 drops). Pipettes are available from chemical and lab supply houses in a range of sizes, along with accessories, such as pipette stands and pipettors (suction devices that draw liquid into the pipette without risking ingestion from pipetting by mouth).

I recommend making early prints using 4x5 negatives to save on materials while you get the hang of the process. For your first print, you'll need about 24 drops of coating solution if you are brush coating (about 18 drops for rod coating). The coating mixture is always one-half metal salt solution and one-half sensitizer solution, and I recommend using equal parts of each of the four solutions for your first print. So, you need six drops of platinum, six of palladium, six of plain sensitizer, and six of the sensitizer with restrainer (four or five of each, if you are rod coating). The order of mixing the components doesn't matter, but make sure to use a separate dropper for each bottle and don't get them mixed up, or you'll risk contaminating the solutions. Once all the solutions have been added to your shot glass or medicine cup, just gently swirl to mix.

Mixing and coating can be done in normal room light, but avoid working under fluorescent lights or in an area where strong sunlight is flooding in. I usually coat in the evening under "romantic" lighting conditions—a covered incandescent bulb overhead, dimmed to the point where I could still easily read if I wanted. Platinum exposures can run five minutes or more in bright sunlight, so all we are really concerned about is keeping fogging to an absolute minimum. Also, don't mix more coating solution than you need, because it will not stand up to storage, even in a light tight container.

As you progress in the platinum learning curve, you'll want to modify the standard solution (equal parts of all four components) to control contrast and tonal temperature. In general, a higher proportion of restrained sensitizer solution will increase contrast, and more palladium gives warmer tones. That said, the variables are much more complex in real life. (As always, Dick Arentz's book on the subject will help fill in the details as you advance.) My current standard is 10 parts palladium, 1 part platinum, 10 parts plain sensitizer, and 1 part restrained sensitizer. My negatives are built around that formula, and I modify the proportions when necessary to accommodate the image.

But no matter what, the ratio of metal salt solution(s) to sensitizer solutions(s) is always 1 to 1 (equal parts of metal salt and sensitizer in the final solution). Otherwise, you are just wasting whichever component is used in a higher proportion.

Coating the Substrate

To prepare for coating, clean your work surface (I use a sheet of glass), place your brush in a cup of distilled water to soak for a minute or two (this keeps the brush bristles from soaking up an excessive amount of the coating solution), and mark the outline of your negative on the substrate you'll be using. Some folks tape the substrate to their work surface, but I've found I can hold it well enough with one hand and coat with the other. You'll also want to have a couple of paper towels handy for cleaning up spills and drying your brush.

For brush coating, I first dry the brush on a paper towel until it is just damp. Then, I pour the coating solution onto the substrate, spiraling out from the center. Working out from the center, I rapidly and lightly brush the coating from side to side (don't worry about going outside your boundary lines), spin the substrate 90°, and brush side to side from the center out, again. That's it! You should have a fairly even coating over the entire image area. If not, don't keep going back over it—you'll just abrade the surface of the substrate. Remember, practice makes perfect, so don't be too concerned if your first few attempts aren't spot on. They will still be good enough to make test prints and sort things out.

Rod coating can actually be easier and give better results, but it is not as intuitive for most folks as brush coating. (Note: These are "right-handed" instructions. If you are left-handed or my directions don't feel comfortable when you attempt to follow them, try swapping left for right and vice versa, where ever those terms appear.) To begin, wipe the coating rod down with a clean paper towel and place it just beyond and parallel to the left border with the handle to the left. Then, rapidly pour the coating solution in a line just to the right of the coating rod, lift the coating rod handle with your right hand, and using gentle downward pressure, draw the rod across the substrate to a point just beyond the right image edge. Now, flip the rod handle over to your left hand (without moving the rod), lift the rod slightly and move it just right of the line of coating, and draw it back across the paper, pulling the line of coating with it. Draw the coating back to the right one more time, and you should be done. At this point, I usually brush any excess coating back into the image area with a dry hake brush, but you can also either leave it to dry or gently mop it up with a paper towel or clean cotton swap.

Now, you should have a fairly even orange/brown coating over the entire image area, and you must let the coating dry before proceeding. If the coating is even damp, it will damage your negative during printing. I live in the land of dry heat, so I just stack coated paper in a large drawer and allow it to dry overnight. In more humid climates or if you are in a hurry to print, you may need to help things along a bit. A blow dryer (for hair) set on its lowest speed and coolest temperature can be used, but wearing a dust mask to capture any stray coating particles is advisable. A print drying cabinet will also work, but no matter what heat source you use, be careful not to overheat the coating.

In my low humidity environment, pre-coated Platinotype paper will keep for two or three days, but I try not to coat anything I won't be using within the next 12 to 24 hours. The longer it sits, the more it fogs and the harder it is to clear the image. In very humid environments, coating shortly before printing is probably advisable. If you want to know for sure how long coated paper (or another substrate) will keep where you live and work, coat and dry one sheet, cut it into strips and try printing partial images on individual strips hours or days apart. The processed and dried strips will graphically demonstrate the dried coating's shelf life and how time affects its printing properties. Keep in mind, however, that different coating formulations will have different shelf lives.

Cleanup after coating is easy. Just wash all your tools with water and dishwashing liquid and let them air dry. I work the detergent deeply into the brush's bristles and thoroughly rinse it under running water (it will be stained, but clean). Then, I shake out the excess water, straighten and flatten the bristles, and wrap the bristle end in a folded paper towel. Pipettes can be a bear to clean, but you'll figure it out, if you choose to use them. Don't worry about cleaning the droppers—just use them to seal their respective bottles.