There has recently been some misinformation broadcast about shellac and its use on collodion plates. While many current practitioners of collodion photography have heard my line on shellac before and many of you use shellac regularly to finish your plates, there are new platers who have not and are going to grow up thinking that shellac is newfangled, non-traditional, non-archival, inappropriate, and generally harmful and evil and should be avoided like the plague for “traditional” sandarac. There could be nothing further from the truth.
So in the interest of disseminating accurate information and setting the record straight, I offer you the Straight Dope on Shellac Varnish for Collodion Plates, supported by proper documentation and evidence rather than merely asserted by bloviating unfounded opinion. And there are tips to using shellac along the way.
1) What is shellac? Is it really “bug shit”?
Shellac is the processed form of a resin secreted by the lac beetle (Laccifer Lacca) and deposited on trees, mostly in India where 70% of the world’s shellac is produced. The word “lac” comes from the Sanskrit word lākshā‘, which designates “100,000” and in this context alludes to the vast number of lac beetles it takes to produce shellac (about 100,000 for 1 kilo). This is the lac beetle life cycle that produces the sticklac that is harvested from trees for processing:
As the immature nymphs suck the tree’s sap, they immediately exude a mixture of resin and wax through their bodies, forming a protective cell reminiscent of a cocoon. Male cells tend to form lengthwise on the branch, while female cells form across the length of the branch, and they can thus be identified. Within these cells, the insects moult several times before maturing, losing their legs, eyes and antennae along the way. While the male’s eyes and legs grow back upon maturation, the female remains an amorphous shape, filling the entire space of her cell, only her back end being situated by an opening, available for copulation. Once mature, the males emerge from their cells; seek out and impregnate the females, shortly after which the male’s mouthparts atrophy, and they die. After this stage of copulation, the female insects continue producing great amounts of Lac resin, and their cells become several times larger than those of the males. This production continues until the female’s own eggs are mature, when she shrinks in size and lays her own larvae, which then hatch and escape, swarming new shoots to start the cycle anew. One female insect can produce between 300-1000 larvae.
(Juliane Derry, “Investigating Shellac: Documenting the Process, Defining the Product,” M.A. Thesis, Oslo, 2012)
Is, then, shellac “bug shit”? That kind of depends on your definition of “shit.” The exudant (secretion) is as much “bug shit” as honey is “bee vomit.” I’d rather like to think of shellac as the product of a lot of lac beetle love. And if calling shellac “bug shit” is intended to denigrate it and make you feel yucky handling it, just know that lac has a long and elite cultural history as coating, thermoplastic molding material, cosmetic, and medicinal. It is mentioned in the 3000-year-old Hindu scripture the Mahabharata (wherein a great palace is constructed entirely of lac) and Roman natural philosopher Pliny the Elder included it in his 77AD Naturalis Historia (Derry, 18). Also know that you probably ate some bug shit today in the form of a shellac coating on a candy or pharmaceutical or in some other processed food where it is commonly used as a coating. About 50% of the world’s shellac goes into food and pharmaceuticals (Derry, vi).
The harvested waxy resinous lac undergoes processing depending on the final type of shellac being produced (it involves heating and/or steaming and drying and filtering), leaving mostly resin and some wax content in a flake or button form. It can be further processed to produce different hues and to remove the wax. Archer’s Envy is made from dewaxed platina shellac, the lightest commercially available shellac outside of the chemically bleached shellac used as coatings in the pharmaceutical and food industries. Chemically bleached shellac is NOT good to use as a varnish because the sodium hypochlorite used for bleaching shellac leaves trace chlorine that will harm collodion over time. Many mid-nineteenth century collodion varnish recipes call for bleached (or “white”) shellac—it was considered as producing THE best varnish because of its clarity and hardness, but that was before it was recognized a generation later that bleached shellac had harmful long-term effects on collodion.
2) “Get out! Shellac is that stuff my geezer granddad used on wood; they didn’t use it on collodion plates back in the day—they used sandarac! That’s what I learned from the guidebook, workshop and the guy on YouTube.”
I didn’t name my latest greatest shellac-based varnish “Archer’s Envy” for nothing. From The Collodion Process on Glass by Frederick Scott Archer (Second Edition, 1854):
So, indeed, they used shellac way back then. I agree with Mr. Archer’s appraisal and recommendation, but with one proviso and one note. The proviso: remember the bleached (white) shellac I mentioned above? That’s what Archer is referring to here and we can’t blame him for not knowing that 25 years hence there will be noticeable problems on plates varnished with “white lac.” In 1880, for example, notable collodion expert Dr. Paul E. Liesegang goes out of his way to specify “unbleached shellac [Ungebleichten Schellack]” is his shellac-based varnish. Here is his recipe and commentary (Google translate it for laughs) if you want to try it. It’s quite good, but I thought too thin and runny, so when I used it as a basis for the original ÜberSuperBlonde (ÜSB) Shellac Varnish, I raised the volume of Schellack to 110g (note the 30ccm Lavendelöl hinzu; I raised that to 50ccm; shout out to Peter Kunz for providing a copy of the original text):
The one note to Archer’s commentary is that I would emphasize the “gently” in his precaution that “the plate should be gently warmed previously to pouring on the varnish.” In fact, I advise pouring on the shellac varnish with the plate and the varnish at a comfortable room temperature without warming at all—only gently warm plate if you live in cold, gloomy, and pre-central-heating England like Archer did. If the plate is too hot when pouring shellac you run the risk of the leading edge of the pour to form a line on the plate if you hesitate and the leading edge stalls. Think of it as a kind of premature flash drying that leaves a mark. When I varnish in relatively cold environments I’ll rub the back of the plate with my hand to gently warm it or perhaps very briefly hold it over my heated griddle.
In addition to the ample historical literature listing plenty of shellac-based varnish recipes for collodion positives and negatives, there is scientific evidence that suggests that shellac was not only used on collodion plates since the 1850s, but that it was a dominant form of varnish throughout the period, eclipsing sandarac. In her 2014 article “The varnished truth: The recipes and reality of tintype coatings” (Journal of Cultural Heritage, vol. 15 issue 1, Jan-Feb 2014, 57-63), art conservation chemist Dr. Corina E. Rogge analyzed the coatings on 221 North American tintypes using pyrolysis gas chromatography-mass spectrometry, zeroing in on five resins: shellac, Pinaceae, sandarac, camphor, and dammar. While the aim of her analysis was to measure the level of correspondence between published historical varnish recipes and the varnishes actually used (only a 24% correspondence), in the course of her analysis it become plainly evident that there was a high preponderance of shellac used (straight or as primary component in a blend of resins). Of the 221 samples, shellac appeared in 149 (16 pure) and Pinaceae-derived resins (most likely Canada Balsam) appeared in 173 (1 pure). Sandarac appeared in 79 samples and never by itself. A table summary of her results (Rogge, page 60):
Rogge hypothesizes that the predominance of both shellac and Pinaceae resins might correspond to use of inexpensive, available commercial varnishes whose unpublished proprietary formulas would also account for the disparity between published recipes and actual use. Other historical literature I have read strongly indicates that the most popular commercial photographic varnishes, such as Anthony’s Diamond Varnish, were indeed shellac-based. If you would like to read Rogge’s entire analysis, I’ve uploaded it under “Files” on the Collodion Bastards Facebook page as “rogge-thevarnishedtruth.pdf.”
3) “How do you make a varnish from bug shit—I mean from lac beetle love?”
As with most synthetic and natural resins—whether from lab shit, tree shit, or bug shit—you dissolve the resin in a solvent to form a spirit-varnish, which is a varnish that operates by evaporating the solvent after its application on the surface being coated. That’s why Archer in his commentary above mentions heating the plate after application—definitely always do that! In essence, the solvent (ethyl alcohol—ethanol—in the case of shellac) transforms the resin into a spreadable liquid for use and then through evaporation the solvent disappears, transforming the liquefied resin back into a hard solid. This basic principle of spirit-varnishes is exceedingly important to understand if you want to be in command when varnishing and understand how and why things can go wrong.
4) “What do you mean, ‘How and why things can go wrong’? I thought shellac was perfect; you and Archer said so.”
We said no such thing. As with anything worth doing, knowledge of your tools and practice of your technique matter. Outside of the precaution to warm the plate only gently or not at all before pouring on shellac varnish, pretty much all other issues with shellac are those shared with sandarac or most any other resin. The good news is that on the whole, shellac is less prone to problems that are frequently seen with sandarac, and shellac has a few useful properties that make it naturally more attractive to use than sandarac. At least Dr. Liesegang and a bunch of Germans commissioned to study negative varnishes in 1870 thought so. The conclusion of that commission (published in Photographische Mittheilungen, 1870, Band 7, p.133—another shout out to Peter Kunz) was that varnishes with sandarac as a main ingredient were unsuited for negatives; they praised mastic mixed with shellac and sandarac as well as light-colored shellac as excellent varnishes for negatives.
So what problems might you encounter when varnishing? Here are the biggies that I often hear:
a. “The varnish melted my plate”
No, your weak collodion committed suicide-by-varnish. Old weak collodion can’t stand up to the alcohol solvent in the varnish, any varnish. This is not a problem specific to shellac varnish. Adding water to dilute the alcohol content in the varnish can mitigate this problem, as the German Commission on Negative Varnishes alludes to in its report when it notes that it’s important to add water to the varnish as pure ethanol can dissolve the collodion. But the better solution is fresh, properly made collodion.
b. “The shellac dried matte over time”
This is the biggest load of bug shit I have ever heard—and I did hear it on YouTube. Let’s get a few things straight. First, while there are a few ways any varnish can dry matte (dull, dead), in the case of shellac, turning dull over time isn’t one of them. In fact, compared to other resins, shellac is UV-resistant and thus doesn’t yellow like dammar does over time. There is no mechanism to make shellac go matte “over time” unless perhaps you deliberately introduced some foreign substance to it.
The type of matte finish one usually encounters involves a thin area (the side opposite the pour-off corner 99,999 times out of lākshā‘) drying in the air prematurely, before heat is applied to the plate to evaporate the solvent. This appears to be more prone with shellac because the relatively thin blends used to coat collodion plates naturally dry more quickly in air. The quick-drying is an asset for lots of reasons (can handle sooner after varnishing, less time for particulates to get embedded in it, less work time), but it turns into a liability if you dillydally pouring off and/or haven’t optimized your technique. Minimizing time pouring off has more overall effect in avoiding a dull edge, but there are little things in technique that help too: pour off at a shallow angle so as not to drain varnish from far edge too thin; use the double pour-off corner technique (pour off about 2/3s one corner and then the rest off the opposite); after pouring off, wick aggressively and swiftly with paper towel and the plate at very shallow angle (to avoid pour off line flowing back); keep your eye on the far edge and when you see the first hint of drying, apply heat to evaporate alcohol to minimize or even avoid a matte edge.
Now, if you do all that and you still get a matte edge, all is not lost—as with woodworking, multiple layers of shellac are better than one thick layer. Which is to say, you can apply a second coat—and do it switching final pour off corners—and 99,999 out of lākshā‘ times, problem solved. Shellac’s structural ability to take a second coat seamlessly (layers naturally fuse together without a trace) is a one huge advantage over sandarac, which does not take well to a second coat. On the other hand, it is generally easier to remove sandarac from a plate than it is to remove shellac (unless the shellac job was fresh) if you want a do-over. But who wants to get into that mess? I’ve done it many times during testing and while it does work with both, I can attest to its messiness.
But why does premature drying in air make varnish go matte anyway? The answer gets us back to the basic composition of spirit-varnishes. In the case of shellac, the usual solvent is about 95% alcohol, with the other 5% being water (“grain alcohol” like full strength Everclear; purer alcohol runs the risk of being too strong for the collodion, even fresh collodion). The evaporation rate of that 95% of alcohol is considerably faster than that 5% of water. Why does that matter? It matters because of the uneven evaporation rates of alcohol and water. The alcohol part of the solvent can evaporate relatively quickly in room temperature air without heat being applied, but when that happens water is left in the shellac by itself and shellac and water do not mix—water can dull and even cloud up shellac. What you are doing when you apply heat to evaporate the solvent and raise the gloss is forcing the 95% alcohol and 5% water to evaporate at effectively the same time. The water departs with the alcohol, thus restoring the resin to its naturally glossy self. Leaving a shellacked plate to dry at room temperature will turn out unevenly glossy or even completely dull all over, and probably cloudy and bumpy as well. Just plain ugly.
Now you might be thinking, logically, that more heat will mean less chance for dull finish and consequently higher gloss. Yes and no. There is a point of diminishing returns at which your beautiful high gloss finish gets pockmarked or blistered because you basically started to boil the varnish. Short of actually boiling the varnish, what starts to happen at a microscopic level is that the heat can start what I’ll simply call micro-convection currents that rise and fall in the varnish, stirring it up in a way that creates micro-calderas in the surface. Any kind of imperfection like that will also look matte as light is being scattered and diffused in the resin as well as being disrupted by the surface topography of the resin. Gloss ( = mirror-like reflection ) is a function of the refractive index of the material, the angle of incident light, and surface topography. Mess with those things and your gloss goes bye-bye. You can read about the math behind this on Wikipedia.
c. There is no c. Like Mary Poppins, shellac is practically perfect in every way.
5) “Maybe so, but still, shellac isn’t the normal, traditional, period-correct varnish to use on collodion plates. Sandarac is, plus it sounds more exotic than ho-hum “shellac”. The guidebook, workshop, and YouTube guy said so. They said so many times. They must be right. And who are you anyway to say differently? You haven’t published a guidebook, given a workshop, or have a YouTube channel.”
Have you been paying any attention at all!? I answered this already. Why do you persist with this misguided belief?! As noted above, shellac has been around since the birth of the collodion process—Saint Frederick himself recommended it. The historical literature is replete with shellac recipes. There are hundreds of surviving shellacked plates from back then that still look great now. Through my personal correspondence with Dr. Rogge—author of that 221 tintype varnish study—I learned that the number one cause of deterioration of plates she has seen is humidity, likely from improper storage. It didn’t matter what varnish was on them. But she has also confirmed through her analysis that shellac was very widespread and, contrary to the guidebook, workshop, and YouTube guy, likely more normal than sandarac, usually as the primary resin with secondary resins like sandarac and Canada Balsam added. Dr. Rogge (a real scientist) analyzed her samples with pyrolysis gas chromatography-mass spectrometry, for crying out loud! Now THAT’S science, not unsubstantiated opinion from a pretend scientist, or even “alchemist.” And by the way, the collodion process is not alchemy and you are not an alchemist (the title of my next Collodion Bastard essay….)