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S e = concentración del efluente en mg/L, es igual a 25,7 mg/L.

3.2. Cálculo de las correas 1 Cargas a soportar

This section presents a list of the categories of photographs you’ll be most often asked to restore, roughly in order of commonness, based on my experience. Prints:

Amateur snapshots, mid-20th century to present

B & W

Color

Commercial and school portraits, mid-20th century to present ● B & W Color Polaroid ● B & W Color Peel-apart SX-70 style

Old photographs (pre-1930s) Professional photographs “ Digital ” prints Slides: Kodachrome Other slide fi lms Negatives: Color B & W Film Glass plate Newspaper clippings Prints

B & W Amateur Snapshots, Mid 20th Century to Present

There ’s a good chance that the photo won’t be badly stained or faded, but it will probably be somewhat low in contrast, with grayish blacks, because that’s what the B & W photofi nishers usually delivered. The color of this era is often nice and neutral, but cheap albums take their toll, so many older photographs are brown or yellow where the silver image has broken down ( Figure 1-9 ).

Prints from the 1950s and 1960s will likely have some cracks from mishandling. Early resin-coated (RC) prints may have lots of fi ne cracking and crazing due to deterioration of the plastic layer carrying the image. Displayed RC prints may have severe silvering out and bronzing problems; that is, there will be shiny or yellowish

patches on the surface of the print ( Figure 1-10 ). Selective masking of the damaged areas (see Chapter 7, “ Masking Methods, ” page 227) works great on this problem. Color Amateur Snapshots, Mid 20th Century to Present

The more recent the photograph, the better the color will be. If they haven’t been on display, prints less than 25 years old won’t be too badly faded. They’ll have Fig. 1-9 Mid-20th-

century B & W photographs may show some yellowing and mild tarnishing, damage that is easy to repair using the techniques from described in Chapter 9.

Fig. 1-10 B & W resin-coated (RC) prints can suffer serious silvering out and bronzing. The masking techniques in Chapter 7 work well for selecting this kind of damage for repair.

lost some density and saturation, but it won’t be hard to bring them back with a good scan. If you get prints that young to restore, it’s more likely the restoration is needed because of physical damage rather than fading.

Older prints will have faded; prints from the early 1970s will mostly be seriously damaged, and those from the 1950s and 1960s might appear hopeless at fi rst glance, looking almost blank, like Figure 1-7 . As you’ll learn, it’s amazing what good scans and digital techniques can recover even in those “ hopeless ” cases. Expect to see some uniform highlight stain in all older color prints.

Photographs that have been on display are another problem entirely; by the time they’re sent to you, they’ll probably be seriously faded. Textured papers, which were very popular in many periods, obscure the image. I discuss some tricks for dealing with them in Chapter 8, “ Damage Repair ” ( Figure 1-11 ). B & W Commercial and School Portraits, Mid 20th Century

to Present

The situation with commercial and school portraits isn’t much different than it is for amateur snapshots, but these prints will have better contrast and tonality than their amateur counterparts. The most likely kind of damage you’ll see in younger prints will be physical problems such as cracking, tears, and dirt. The farther back you go, the more the prints will be stained, but the staining is often uniform and so is easy to correct. Unfortunately, the average quality of older print processing was much poorer. Although quite a few are still in good shape, you see many portraits from the 1930s to early 1950s that have stained and turned brown or even yellow.

Color Commercial and School Portraits, Mid 20th Century to Present

The average quality and problems are no different from those you’ll encounter with amateur photographs. Low-cost commercial and school portraiture was very

Fig. 1-11 Color portraits are often printed on textured paper that obscures the scanned image. Chapter 8 shows you how to eliminate that textured surface from the restoration.

variable in quality. Some school photographs from 30 years ago look surprisingly good; others have changed color in all sorts of bizarre ways ( Figure 1-12 ).

Textured paper was very common, almost ubiquitous, for many years. The more faded the color photograph, the more intrusive the texture will be after you restore it; the increases in contrast you make to restore the color also increase the contrast of the texture pattern. Expect to have all the problems you would encounter in restoring an amateur color photograph, plus you’ll have the paper texture to contend with.

B & W Polaroids

Most B & W Polaroid prints needed lacquering to keep the silver image from quickly oxidizing. The condition of old B & W Polaroid prints depends on how well the photographer coated the print ( Figure 1-13 ). You’ll see prints with streaks where the well-lacquered portions still have good neutral B & W tones and the poorly coated streaks have faded to brown or yellow. Selective masking is one way to isolate those areas, but sometimes clever channel mixing will do the trick (see Chapter 7).

I don’t know whether it’s because of their small size or stiffer paper, but Polaroid prints are usually less cracked or torn than conventional photographs of the same vintage. You’ll need to put in more work correcting uneven fading on these than repairing physical defects.

Fig. 1-12 Cheap school portraits come in a variety of (very wrong) colors. Digital restoration, using the methods in Chapter 6, can do a remarkable job of restoring the original color.

Color Peel-Apart Polaroids

The peel-apart Polacolor prints have fairly stable dyes when the prints aren’t on display. Prints from the 1960s and 1970s have usually faded much less than their conventional color counterparts. Polacolor color and tonal quality were not very good, though, so you’ll almost always want to go the extra step in restoring these photographs to make them look better than they originally did (see Chapters 9, “ Tips, Tricks, and Enhancements, ” and Chapter 10, “ Beautifi cation ” ). Expect older prints to have a greenish cast to them, especially in the highlights and skin tones, and whites will be far from true white ( Figure 1-14 ). Mostly you’ll be repairing physical damage and improving the tone and color quality over what

Fig. 1-13 How much B & W Polaroid prints fade depends on how well they were coated. These two prints both date from the same year in the late 1960s and were found in the same album.

Fig. 1-14 Peel-apart Polacolor prints fade very little when they’re kept in albums. The poor color of the original photograph is normal for this type of print; careful scanning and color adjustment can make it look better than new.

they originally were. Simply making a carefully adjusted scan will often get you pretty good color.

Prints that have been displayed are another matter. If they’ve been exposed to light, Polacolor prints fade just as badly as conventional ones, and sometimes worse.

Color SX-70-Style Polaroids

Just like the peel-apart prints, SX-70-type prints hold up well in the dark but poorly on display. They acquire a yellowish highlight stain pretty quickly under all conditions, but it’s usually uniform. Color improved with each successive generation of these materials, but it was never as good as conventional color prints, so my comments about improving the color of Polaroid prints apply here.

Because of their sturdy protective shell, these photographs usually won’t be cracked, torn, or dirty, but they are subject to internal damage. Some older SX-70-style prints develop internal cracks, crazing, or a fi ne frost-like pattern that obscures the image ( Figure 1-15 ).

Old Photographs (Pre-1930s)

These “ vintage ” photographs will almost always be B & Ws. The whites invariably darken and turn anywhere from pale tan to dark brown. The image itself may be faded, so the overall contrast can be extremely low. The damage is often very non-uniform, so you’ll have to make local corrections to the tones as well as overall ones. Dodging and burning masks (see Chapter 5, “ Restoring Tone ” ) are of considerable help.

Fig. 1-15 Some Polaroid SX-70 prints have suffered internal damage. Repair them the same way you would a photograph with fi ne cracks or scratches on it (see Chapter 8).

All the photos will have some degree of physical damage ( Figure 1-16 ). Restoring the tonal range of a low-contrast photo exaggerates the fl aws; in extreme cases you’ll be dealing with “ noise ” that is almost as strong as the “ signal. ” Very old photographs are often missing pieces of the emulsion that will need to be recreated to make the photograph look good again.

Many of the photographs will have “ tarnished out ” ; there will be shiny metallic-looking bronze or silver patches on the surface of the photograph, especially in higher-density areas ( Figure 1-17 ). You’ll do best to attack those with selective masking (Chapter 7, “ Making Masks, ” page 227) so that you can correct those

problems separately from the rest of the photograph. Chapter 8, “ Damage Control ” (page 281) , tells you how to repair tarnish.

You ’ll see a fair number of hand-tinted B & W portraits. They will present you with challenging questions, not technical in nature but artistic. If the goal is to produce a good-looking, hand-tinted portrait, modern tastes and sensibilities around such work are very different from those of 50 – 100 years ago. By today’s standards, you may get a more pleasing photograph by eliminating the tinting entirely (not diffi cult) and turning it into a straight B & W photograph.

Fig. 1-16 The older the photograph, the more likely it will be physically damaged. At the very least there will be dust, dirt, and scratches; in many cases there will be cracks and tears.

Fig. 1-17 Severe cases of tarnish can be quickly and effectively repaired. Chapter 8 shows you how.

If your objective is to produce an historically accurate restoration, you’ll need to know a lot about the tools and techniques, not to mention the aesthetics, of the era in which the photograph was made. The tints you see in the damaged photograph will not be representative of the original hues, and anything that you do to restore proper tone and contrast and eliminate stain and yellowing will alter the colors in ways you can’t predict.

Professional Photographs

Professional photographers usually took better care of their photographs than amateurs, and the photographs were usually made with more care and were processed better. Until we get back into the “ vintage ” era, professional photographs for the most part look better than comparable amateur ones. The most notable exception is that color prints will fade regardless of how well they were processed (although the poor processing used for many cheapo commercial portraits signifi cantly accelerated their fading), so old professional color prints may look just as bad as amateur ones of the same era. Except for color dye fading, though, you’re more likely to get a modern professional photograph to restore because it’s suffered physical damage than because it’s badly in need of tone and color correction.

“ Digital ” Prints

The overwhelming majority of photographic prints made today are printed with the assistance of a computer. Most of those prints made by mass photofi nishers, though computer-driven, are still made on traditional chromogenic color print paper. They don’t present any novel restoration problems. In the future, though, that will change because some fl avor of inkjet printing will take over.

Small -scale commercial printing and home printing use different media and technology. Inkjet is the most common, with second-place going to dye sublimation, a.k.a. thermal transfer or dye transfer. (This is not to be confused with the traditional darkroom process known as dye transfer printing; they are entirely different beasts.) A very small fraction of prints come off color laser printers or solid-ink printers such as those made by Tektronix/Xerox.

It ’s easy to distinguish inkjet prints from dye sublimation prints (which we’ll discuss in Chapter 2, Figure 2-11). Examine the print with a good 10 loupe. If you see a random pattern of fi ne dots, it’s inkjet. If you see a pattern-free, continuous- tone image or a regular grid of continuous-tone square pixels, it’s dye sublimation. In the unlikely event you encounter a laser or solid ink print, what usually sets it apart is that magnifi ed viewing will show a pattern of fi nely spaced, distinct lines.

Dye sublimation prints, except for the very earliest ones, have an overcoat layer for protection. This gives them a uniform surface fi nish. It makes it easy to distinguish them from laser or solid ink prints, which will have a pronounced surface relief but usually won’t show a giveaway random dot pattern the way inkjets do. Inkjet prints may or may not show a surface relief, depending on the specifi c printer and paper used.

Incidentally , “ giclee ” is just a hoity-toity synonym for inkjet. There was a very short period of time about 15 years ago when it denoted a particular kind of inkjet print. Nowadays the term is used by printers simply to make their work sound fancier than the norm; it’s functionally equivalent to saying “ deluxe ” or “ acme. ” It has no signifi cance for us restorers.

Digital prints are subject to the same kinds of damage that traditional color prints are, with a couple of extra “ gotchas ” thrown in. Some types of inkjet prints were easily damaged by water, which would cause the inks to bleed; that’s a problem that traditional and other digital prints won’t have.

Though digital prints are subject to light fading just as conventional prints are, many of them were also attacked by airborne chemicals. Light fading is usually proportional, with the areas containing the most colorant fading the most and the ones with the least fading the least. That’s why it’s possible to do such an excellent job of restoring full color to faded prints; there’s almost always some measurable density over the entire tonal scale.

Chemical deterioration, though, is often subtractive. That is, it removes equal amounts of density from all parts of the image, no matter how light or dark the areas were to begin with. That means that low-density areas can completely lose detail in a way that won’t be recoverable through simple curve manipulations and contrast enhancement ( Figure 1-18 ).

Digital prints are heir to physical damage, just as traditional prints are. Nothing new there; you’ll be dealing with the physical damage the same way regardless of the nature of the print.

Slides Kodachrome

I ’ve never seen a badly faded Kodachrome slide, and neither will you, unless it’s one that has been projected a lot. Kodachrome dyes are extremely stable in the dark, although they fade rapidly in the light. If you get a Kodachrome slide to restore, it will probably need very little tone or color correction

( Figure 1-2 ). More probably you’ll be asked to restore it because it is physically damaged. Water and mildew damage repair are common restoration jobs; occasionally you’ll come across a slide that’s been mishandled and badly scratched.

Other Slide Films

Recent non-Kodachrome slide fi lms are pretty stable. As with Kodachromes, you are more likely to be doing restoration work to correct physical damage than fading. Go back to the 1960s and it’s a different matter; just as with color prints, you’ll be looking at slides that have faded or stained. Slides from the 1950s will be in extremely poor shape. If they aren’t brick-red ( Figure 1-19 ), they will be very badly darkened and stained.

In either case, color correction tools like DIGITAL ROC can work miracles. The hard part will be getting a good scan. Most of the slides will have one or more dye layers that have faded very little, so the overall density range in the slide can be quite high. See Chapter 4, “ Getting the Photo into the Computer, ” and Chapter 9, “ Tips, Tricks and Enhancements ” for ways to deal with this issue.

Negatives

Even though the majority of photographs made in the past 50 years have been negatives, most of the time you’ll work on a deteriorated print. Usually that will be because the client doesn’t have the negative, but it never hurts to ask. Original negatives, B & W or color, almost always permit better restoration than the prints made from them.

Fig. 1-18 Early inkjet prints (and those made even today with cheap third-party inks and paper) are widely susceptible to both light fading and chemical attack, causing odd color shifts. Here the black ink has faded to tan. The difference is very evident in the enlarged edge of the print, where a thin strip was shielded from light by an overmatte. The black dots in that strip are much darker.

Color Negatives

This is not to say that negatives don’t deteriorate. In fact, color negative fi lms are among the least stable of all types of fi lms, and older ones were especially bad. Physically the color negatives are likely to be in pretty good shape; they’ve probably never come out of their folders and sleeves since they came back from the photofi nisher. You won’t have unusual numbers of scratches and dirt specks to clean up.

The most common physical damage I see in old color negatives is due to poor processing. There may be long scratches down the fi lm, or water spots; sometimes there are surge or fl ow marks where the developing chemicals didn’t bathe the negative evenly. Mildew damage is a less common occurrence.

Most of the time you will be faced with a clean but uniformly faded negative. Your task will be to fi gure out the major tone and color adjustments needed to produce a correct-looking print. There will be serious dye loss; the fading will be at least as bad as with very old color slide fi lms. Color correction will be a