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Architectural photoreproductions : a manual for identification and care /Eléonore Kissel; Erin Vigneau

1999 1st ed. English Book ix, 121 p. : col. ill. ; 26 cm. New Castle, Del. : Oak Knoll Press ; Bronx, N.Y. : New York Botanical Garden, ; ISBN: 1884718620 9781884718625

Summary This volume written to aid the archivist in how to identify the many varied architectural and structural reproductions, how they were created, and the correct storage methods for each type of material to better preserve the materials.

This book is intended for anyone who has architectural plans, whether a group of 20 or 20,000. The manual is designed to be used by individuals with no special training in preservation, photography, or architecture. Purposely created method of identification based solely on visual examination. It covers reproductions which were commonly used in North American architectural practice from 1860 to 1960.

Many collections from the 20th century include blueprints, but also closely related positive blue prints and Pellet prints and brown images such as Vandyke and ferrogallic prints, diazo prints in magenta, blue, black, brown, and lavender. Many prints will also be annotated in pencil, ink and colored crayons on tracing cloth, polyester film, translucent tracing and vellum papers, and medium weight opaque papers.

Generally produced on paper or drafting cloth (usually cotton or linen) using photosensitive chemicals that are altered when exposed to light. Often “wet-processed” (immerse in developing bath, sprayed with a developing solution or exposed to developing vapors). Because of these procedures, often have chemical residues embedded in the paper or cloth, or on the surface. For this reason, often require unbuffered or polyester envelopes to protect them and to protect adjoining items

A very easy to use book with lots of color illustrations and close-ups of images that can be seen with a magnifying glass.

Detailed Notes

Foreword Pre-1870 – most copies produced by hand usually by tracing onto translucent paper or cloth and pricking through the original onto a new support then redrawing the copy from the pricked points

1870 – blueprints introduced – fast, easy, cheap, and accurate. Papers coated with light-sensitive salts placed directly under original inked drawing and exposed to light. Within decades machines invented to quickly expose, wash, and dry blueprints.

1880 > other photo reproductive processed invented with variety of light sensitive materials including iron, silve, chromium, and diazo salts resulting in wide array of processes on a wide variety of supports.

Many collections from the 20th century include blueprints, but also closely related positive blue prints and Pellet prints and brown images such as Vandyke and ferrogallic prints, diazo prints in magenta, blue, black, brown, and lavender. Many prints will also be annotated in pencil, ink and colored crayons on tracing cloth, polyester film, translucent tracing and vellum papers, and medium weight opaque papers.

Preface Book has flowchart and 12 chapters on individual reproductive processes. Flowchart presents a series of questions based on visual examination which can lead to tentative identification. Criteria include support, image, surface, and overall condition

Glossary (only terms also included in this summary are included here) Negative: light lines on a dark ground Positive: dark lines on a light ground Drafting cloth

Flowchart Very easy to follow. Sometimes results in multiple possibilities, but explanations are very clear.

PART II PHOTOREPRODUCTIONS

Prints produced using photographic process using photosensitive chemicals. The support (paper, drafting cloth, plastic film) is coated with a photosensitive chemical solution. It is then placed on contact with a translucent original drawing or a reproducible master and exposed to light. The chemicals are altered when light shines upon them. The image appears when the print is immersed in a developing bath, sprayed with a developing solution, or subjected to developing vapors. some prints are fixed or rinsed, and some not at all, depending on the substance involved. Prints produced using a photographic process always contain chemical residues embedded in the support or deposited at the surface. These products are generally more unstable than the drawing media used to produce original drawings. The chemical nature should always be kept in mind when dealing with their storage. In order to avoid the risk of contact degredation, the basic rule is to segregate the various types of prints from each other and the original drawings.

Note: most common features, and most basic History and Manufacturing features only indicated. Specifics and rare or less common characteristics not included.

General notes: Paper fibers described as viewed under a loupe of 10x to 30x magnification History and Manufacturing: Where the light is blocked is any part which contains the lines in the image or text. Where the light is exposed is the rest of “blank space” of the image

Aniline Prints (1856 – late nineteenth century, replaced by blueprints – up to 1890s) o Line colors: often purple, blue, or black. o Ground colors: most striking is the green hue. o Positive / Negative: always positive prints. o Contrast: low contrast o Support: paper or drafting cloth. o History and Manufacturing: Prepared with sulfuric acid and the chemical aniline reacting with certain metallic salts to produce colored compounds (aniline dyes). o Degradation: Degrades when exposed to light. Paper may become brittle, drafting cloth may become limp. o Storage: Due to acidity, prints should be separated from other types of prints. o Buffered / unbuffered / polyester: Use unbuffered folders, sheets, or polyester sleeves.

Blueprints (1842 – present, declined in 1930s) o Line colors: white o Ground colors: Prussian Blue, blues can come in varying hues. o Positive / Negative: negative o Contrast: high contrast o Support: Paper or drafting cloth. o Magnified view: easily visible under a loupe, will appear dyed or stained with blue. o History and Manufacturing: Paper support sized usually with gelatin so that the sensitizing solution would not penetrate the fibers too deeply. Support sensitized with equal parts ferric ammonium citrate and potassium ferricyanide, left to dry in a cool dark area. It is placed beneath a drawing made on translucent support and exposed to light. Where the light is blocked the ferric salts are reduced to ferrous salts. Developed by immersing in a water bath and dried. In contact with water, the ferrous salts produce ferric ferrocyanide which gives it the Prussian Blue color. The ferric salts which have not been exposed are washed away during the developing process which leaves the white lines that form the image. Papers come in variety of qualities. Generally lower quality papers after 1920s when machine-made blueprint papers with lower rag count were produced. o Degradation: Degrades when exposed to light. Fading can occur very rapidly (sometimes in less than 1 hour under fluorescent light exposure). High humidity may cause it to turn brown. Paper may become brittle. o Storage: Due to acidity, prints should be separated from other types of prints. o Buffered / unbuffered / polyester: Use unbuffered folders, sheets, or polyester sleeves.

Diazotypes (1880 – present, 1917 pre-sensitized papers produced, 1920 1st dry process with ammonia vapors which led to widespread use replacing blueprints for industrial use – still in use) o Line colors: over 2,000 azo dyes, most common colors are purple, blue, black, brown, and hues of red and green o Ground colors: varied colors, frequently smudged, flecked or “dirty” white. o Positive / Negative: primarily positive o Contrast: ? o Support: paper, plastic film, drafting cloth. Most often found on opaque paper made from cotton or wood fiber. Sensitized drafting cloth may have been used for oversized prints. Since the 1930s pre-sensitized plastic films and translucent papers produced Diazotypes for intermediate prints o Magnified view: Fibers easily visible under a loupe, will appear dyed or stained with blue. Dye formed directly on surface of the paper. o Other: Diazotypes are dry-processed, resulting in a smooth matte surface. Surface of Paper support may turn yellowish brown, pronounced along the edges of the print on the image side. Diazotypes reproduced faint graphite lines, as well as fold and marks which were on the original. o Distinguish from others: Diazotypes are smooth and hard, whereas blueprints and Pellet prints have raised fibers, this is important when trying to distinguish between positive blueprints and Pellet prints from blue line Diazotypes. o History and Manufacturing: Formed by the chemical reaction of a diazo compound with a phenol or napthol based coupler. In the dry process the support is coated on one side with a sensitizing solution containing the diazo compound. The color of the line is largely determined by the choice of coupler. Blue line are produced with a napthol coupler is used. Brown line are produced when a phenol derivative is used. Black line are produced by a mixture of couplers which can yield a reasonably neutral black. The sensitized support is placed beneath an original drawing or a translucent intermediate and exposed to ultraviolet light. Where the light is blocked and the diazo compounds remain intact, forming a dye upon development. Where the light is exposed and the diazo compounds are rendered colorless. Prints are then either dry processed or “semi-moist” developed. Unlike many other prints which are wet processed and washed, a diazotype has residual chemicals left in the paper which may casue degradation. o Degradation: Exposure to ultraviolet light accelerates degradation of diazotypes when the residual phenols oxidize in contact with oxygen. This degradation only occurs on the sensitized rector of the print. The edges which are near the sides of folders or shelves, or when folded, and the folds are exposed to air and light, may also be affected, resulting in edge discoloration. The azo dyes used are unstable in acidic conditions. Because the dry process remains acidic, it is to a degree self-destructing. Paper often degraded and brittle due to residual acids. Poor tear strength and fold and fracture marks can be found, especially if the paper was made from wood fibers. Diazotypes of drafting cloth usually remain sturdy. Diazotypes on plastic film such as cellulose nitrate, cellulose diacetate and cellulose triacetate are unstable because their support is unstable. Common problems are brittleness, yellowing, shrinking, distortion, and oozing of plasticizers o Storage: May still have alkaline vapors off-gassing from the print because of its ammonia development or by the sulfur-based products. Blueprints may be harmed by the alkaline vapors and silver-based prints such as Vandyke prints may be harmed by the residual sulfur-based products. o Buffered / unbuffered / polyester: Phenols oxidize faster in an alkaline environment, diazotypes should be stored in pH neutral folders or isolated from buffered paper by polyester films.

Ferrogallic prints (1860 - 1930, used mostly in Europe) o Line colors: blue-black lines with a metallic sheen, fade to faded black to brown. Ink-like lines o Ground colors: white, discolors over time to pale brown or slightly lavender o Positive / Negative: positive o Contrast: very low contrast o Support: usually paper, some pre-sensitized drafting cloth also commercially available o Magnified view: The image may appear slightly raised o Other: Allowed corrections during processing. o History and Manufacturing: 2 methods. 1st support is sensitized with a solution containing a colloid such as gum Arabic or gelatin and ferric salts such as iron chloride or iron sulfate. 2nd method developed after 1900, the organic acids incorporated into the prepared sensitized support with the ferric salts. Same equipment may be used for blueprints The sensitized paper is placed beneath the drawing made on translucent support (tracing paper or drafting cloth) and exposed to light the ferric salts are reduced to ferrous salts rendering the gelatin water soluble. The ferrous salts and the soluble gelatin in the exposed areas are rinsed away. The unexposed ferric salts held by the insoluble gelatin combine with the tannic acids in the developer to produce a blue-black deposit of ferric gallo tannate which forms the image. Finally rinsed in water to avoid producing a print which will quickly become brittle and unusable due to residual acids o Degradation: the paper is very brittle from the tannic acids and the History and Manufacturing process. The lines themselves are acidic and may actually pierce holes in the paper. Very light-sensitive, lines brown and can face, sometimes disappearing completely. o Storage: Sensitive to alkaline environments, avoid housing in a buffered environment. Use PAT tested storage o Buffered / unbuffered / polyester: Isolate in unsealed polyester film enclosures, use unbuffered support sheets for handling.


Photostat prints (1909 – negative prints, 1953 – positive prints, declined in 1970s ) o Line colors: negative print: white ; positive print: black o Ground colors: negative print: black and range of grays ; positive print: white, range of grays o Positive / Negative: negative or positive o Contrast: high contrast o Support: opaque paper, standard sizes were 12” x 14” to 18” x 24” o Magnified view: The paper fibers cannot be distinguished easily, the image is embedded in an emulsion, surface is slightly glossy o Distinguish from others: appear much like black and white silver halide photographs, although exhibit more contrast, less gray tonality, and no apparent grain when viewed under magnification of 15x o History and Manufacturing: photographic copying machine produced silver based black and white photostatic prints without the use of an intermediate film negative. 1st prints were negative prints, colors would appear in various shades of gray. 2nd prints (1953- ) were positive prints by copying the negative print. The 2nd generation prints were not as sharp. Sensitized paper was highly orthochromatic meaning that it would copy all hues of color. Could be enlarged or reduced quickly and accurately. Given equal status to originals in legal instances up until the 1970s. The original did not have to be on a translucent support in order to be copied. Produced on paper sensitized with a photographic, gelatin based emulsion containing silver salts. The paper is coated with a thin layer of emulsion which consists of finely dispersed silver halide crystals suspended in gelatin. The Photostat paper is prepared in rolls and held in the Photostat machine. The Photostat is a large camera with precise arrangement of focusing scales, copy boards and lamps to control scale and exposure. The machine would then process the print, the exposed print is immersed in an alkaline developing bath which converts the argentous silver into metallic silver, creating the black lines and gray areas of the image. The developed print is fixed in a bath of sodium thiosulfate which dissolves the undeveloped silver halide. The final water bath removes the residual silver halide and sodium thiosulfate from the print o Degradation: silvering or mirroring effect which can be seen in the darker areas of Photostat prints. Brown stains sometimes found on the verso of Photostats due to insufficient washing. Wear gloves to prevent fingerprints from marring the surface o Storage: Do not house with either Vandyke prints which may contain residual sulfure from the fixing bath or diazotypes produced after the 1930s which may contain thiourea. o Buffered / unbuffered / polyester: House in unbuffered paper folders or polyester sleeves.


Positive blueprints and Pellet prints (mid 1800s – declined in 1930s) Described together because of their nearly identical appearances and may be safely stored together o Line colors: Prussian blue in various hues o Ground colors: light o Positive / Negative: positive o Support: paper or drafting cloth o Magnified view: Positive blueprints: fibers easily visible under the loupe, will appear dyed or stained. Pellet prints: blue lines sit within and slightly on top of the paper surface o Distinguish from others: Positive blueprints: ground may contain some blue streaks or spots if an excess of ferrous salts was present during the developing phase and will often have a smooth, slightly blue tone. Pellet prints: ground will have a bright white ground with occasional blue specks. Blue line diazotypes: frequently have flecked blue marks that occur throughout the background unlike the smoother more uniform ground of positive blueprints and Pellet prints o History and Manufacturing: Positive blueprints: same as a blueprint, except that it is placed beneath a negative print such as a Vandyke print. Pellet prints: support is sensitized, exposed, and developed similar to blueprinting, but the chemical process differs slightly o Degradation: same as for blueprints o Storage: Due to acidity, prints should be separated from other types of prints. o Buffered / unbuffered / polyester: Use unbuffered folders, sheets, or polyester sleeves.

Sepia Diazo Prints (1920 – still in use) o Line colors: warm brown o Ground colors: mottled from white to yellowish white to pink, faint orange, or faint blue. The ground is “dirty” or mottled and can vary from a light flecking to heavy mottling that can make the images lines appear almost unreadable o Positive / Negative: positive o Contrast: ? o Support: translucent papers or plastic film, may also be found on opaque paper. The paper retains a calendered surface because it is dry processed o Magnified view: Fibers easily visible under a loupe. Dye formed directly on surface of the paper. o Other: Sepia diazotypes reproduced faint graphite lines, as well as folds and marks which were on the original. Image side is usually slightly shiny and glossy. Some sepia diazo prints have a slick or waxy surface. Often printed in reverse, that is, the sensitized or colored side of the paper will have an image on it that is reverse reading. In order to read the print it must be read through the verso with transmitted light. When stored with tracing paper will cause a pink discoloration on the neighboring tracings. Tracings found next to impregnated sepia diazo prints often have greasy looking patches o Distinguish from others: Sepia diazo prints have a mottled, smudged ground and their lines which are not as crisp. The surface is smooth and hard. Vandyke prints are a cool brown, dense and uniform, and have a metallic sheen. The surface has raised fibers o History and Manufacturing: Manufactured using the diazotype process. Like Vandyke prints used as intermediates. The brown lines of sepia diazo prints are useful for making reprints because they have a high opacity to the ultraviolet light which is used to make subsequent diazotypes. Their use as intermediate prints is popular because they can be corrected by several methods including eradicator fluids, and since 1970, simple erasure. Reverse reading sepia diazo prints allowed corrections to be made on the unsensitized plain paper side of the verso. The use of a sepia reproducible master saved on the wear and tear of making prints from an original drawing. o Degradation: Degradation caused by residual sensitizing chemicals which oxidize and cause the paper support to turn a yellowish brown. This discoloration is always more pronounced along the edges of the print, and occurs only on the image side, i.e. on the sensitized surface. Because of the warm brown tone of sepia diazo prints, the translucency of many of the supports, and the impregnation products used in them, this discoloration may not be as marked as that other diazo based prints. Degrades like all diazotypes with exposure to ultraviolet light o Storage: May still have alkaline vapors off-gassing from the print because of its ammonia development or by the sulfur-based products. Blueprints may be harmed by the alkaline vapors and silver-based prints such as Vandyke prints may be harmed by the residual sulfur-based products. o Buffered / unbuffered / polyester: Phenols oxidize faster in an alkaline environment, diazotypes should be stored in pH neutral folders or isolated from buffered paper by polyester films.

Vandyke Prints (1889 - , 1912, Department of Agriculture established standards that only 100% rag content paper should be used because of the degrading effect of the silver nitrate contained in the sensitizing solution – declined in 1930s) o Line colors: negative print: white ; positive print: brown o Ground colors: negative print: brown ; positive print: white o Browns can vary from a medium value cool brown to a very dark almost black brown o Positive / Negative: negative or positive o Contrast: high contrast o Support: paper, usually light, translucent to medium weight papers. o Magnified view: Produced without an emulsion, therefore the image appears to be embedded in the surface fibers of the paper. Will have raised fibers typical for a process which has a wet development step similar to the surface of a blueprint. o Other: Used as intermediate prints, often when the original is damaged, or when a positive image reproduction is necessary. Intermediate Vandyke prints can sometimes be found with erased areas and pencil or ink notations. The final print is usually a positive blueprint or a positive Vandyke print. Blue staining may sometimes be found on the verso due to the incomplete removal of iron salts o Distinguish from others: see Sepia diazo prints. Vandyke prints not found on paper which has been impregnated with products to make them more translucent o History and Manufacturing: Pre-sensitized Vandyke paper does not expose quickly, therefore this printing process can be used when the original image is faint. Drawback of wet processing means that it is prone to dimensional variations, especially important for prints which are made from Vandyke intermediates. In these instances, the drawn scale becomes virtually unusable. The Vandyke process is based on the interactions between silver an iron salts. The manufacturing process is similar to that used for the production of blueprints, except that an additional fixing bath is required. o Degradation: Vandyke prints contain silver, therefore they are sensitive to sulfure. Residual amounts may remain from the fixing bath, especially if it was not thoroughly rinsed. Generally, Vandyke prints were not produced for permanence, so little can be done about this degredation o Storage: Do not leave on contact with diazotypes. Many diazotypes contain thiourea (a sulfur containing product) which has been found to bleach silver based prints that they are in contact with. The sensitizing solution also has a weakening effect on the paper. Use cotton gloves to prevent oil from fingers marking and damaging the silver based prints. Segregate from other reproductions as well as from original drawings o Buffered / unbuffered / polyester: unbuffered paper folders, polyester sleeves to segregate from other types of prints and original drawings.


Wash-off prints (1920s – declined in 1960s) o Line colors: black and ink like o Ground colors: light, smooth, clean ground with occasional black flecks. Surface of the drafting cloth may discolored o Positive / Negative: positive o Contrast: high contrast o Support: drafting cloth, paper, plastic film o Magnified view: The lines appear to sit high on the surface of the support with a slightly metallic sheen o Other: Often printed in reverse, i.e. the sensitized or colored side of the support has an image that is reverse reading. In order to read the print one must read through the verso with transmitted light. o History and Manufacturing: Produced ink-like substitutes for original drawings. Popular because a clean copy could be produced from a poor original. Surface coated with a gelatin based emulsion which contains light sensitive silver salts. Placed beneath an intermediate negative such as a Vandyke print, and exposed to light. Where the light strikes, the emulsion becomes hardened. The exposed print is washed in water causing the unhardened areas to be removed. The print is developed in an alkaline solution containing potassium hydroxide, and the remaining latent image of silver halide appears in black. The print is rinsed in water and dried. The process allows an operator to clean areas of the ground during processing, thus allowing a clean print to be made to be made from a poor quality original document. It is also possible to remove lines by the use of a moist eraser or a liquid eradicator. o Degradation: The drafting paper may discolor over time. Plastic films produced on cellulose nitrate, cellulose diacetate and cellulose triacetate are likely to degrade because of the inherently unstable nature of these supports. Common degradations include brittleness, yellowing, and oozing of plasticizers. Polyester films used since 1980s are more stable. o Storage: Sensitive to sulfur, therefore should be separated from any print containing residual sulfur such as diazotypes o Buffered / unbuffered / polyester: Store in polyester folders separated from other prints and drawings

PART II PHOTOMECHANICAL REPRODUCTIONS

Print produces using a plate or similar matrix, whereby the plate was prepared using a photographic process involving photosensitive chemicals and light. The photosensitive chemicals are used to produce the plate, not the print. Prints using photomechanical process do not contain chemical residues embedded in the support or deposited at the surface, as they were produced with ink, dye, or carbon particles instead of photosensitive chemicals. These prints are much more stable with properties similar to original drawings on paper, drafting cloth, or plastic film. May be housed in contact with original drawings

Electrostatic (Invented 1938 ; Commercially available 1948 ; 1960 Xerox 914 became widespread in printing firms and businesses – still in use) Direct electrostatic print (“Electro-Fax”): paper coated with zinc oxide. Indirect electrostatic print (“Xerox”): paper or plastic film o Line colors: black carbon-based toner o Ground colors: o Positive / Negative: positive or negative o Contrast: o Support: o Direct electrostatic print (“Electro-Fax”): paper coated with zinc oxide. Appears slick and shiny and is easily tarnished when a small piece of metal such as a coin is run across it. The zinc coated surface cracks when the document is folded or creased. The paper may be fragile due to degradation over time o Indirect electrostatic print (“Xerox”): paper or plastic film. Usually smooth, well calendered paper although almost any medium weight paper can be used. Copies sometimes have dark areas that are striated and uneven o Magnified view: Toner will appear to sit on top of the support o Other: Density is uneven in the dark areas making these processes more useful for the reproduction of line drawings or text than colored drawings, photographs, etc. Prints range in density and contrast in accordance with the original from which they were produced o Distinguish from others: o History and Manufacturing: Uses static electricity to create negatively and positively charged ions which assist in creating the image. Light is reflected from white or light colored areas of the original onto a positively charged photoconductive surface; black areas of the original absorb the light and do not reflect onto the photoconductive surface. o Degradation: Electrostatic films produced on cellulose nitrate, cellulose diacetate and cellulose triacetate are likely to degrade because of the inherently unstable nature of these supports. Common degradations include brittleness, yellowing, and oozing of plasticizers. Polyester films used since 1980s are more stable. o Direct electrostatic print (“Electro-Fax”): The zinc oxide used to coat the paper contributes to its degradation. The copies prouced are fragile as the paper support discolors when exposed to light in a humid environment and may become brittle. Exposure to water will render the zinc oxide coating powdery, destroying the images. They should not be housed in contact with other paper documents. These copies should not be considered permanent records, it is suggested that the information be reformatted. o Indirect electrostatic print (“Xerox”): It all depends on the nature and surface of the support, nature of the toner resin, proportion of carbon in the toner as well as the temperature used for fusing the toner resin. In principle, the prints are stable especially if produced on acid-free paper. However, the image may flake if it is abraded or if the support is physically distorted by folding. Electrostatic prints on plastic film are highly susceptible to abrasion. o Storage: o Buffered / unbuffered / polyester: Unbuffered paper enclosures. Do not store in polyester sleeves or envelopes, images lines that are not fully fused may transfer to plastic film


Gel-lithographs (1900 - used extensively until 1950s when gradually replaced by diazotypes) o Line colors: printed ink, whatever color the ink was o Ground colors: o Positive / Negative: positive o Contrast: o Support: smooth, well-sized paper or drafting cloth. o Magnified view: inked lines are opaque and dense when viewed through a loupe, appear to be sitting on top of the surface o Other: Starch sized drafting cloth of a gel-lithograph may have areas which have lost the smoothness of the sizing due to contact with damp gelatin in the printing process, while edges that were not in contact with the gelatin during the printing remain very glossy. o Distinguish from others: Hectographs lines are composed of dyes which penetrate the surface of the support, Gel-lithographs sit on top of the surface. o History and Manufacturing: Ferric salts produce local hardening when put in contact with gelatin in order to create the gel-lithograph process. Same process used in the Pellet print. A gelatin pad or graph is made to serve as the plate for the gel-lithograph. Gelatin is softened and dissolved in water with iron salts. This mixture is poured into a tray on onto a specially designed table. When the gelatin cools it becomes firm, but retains some moisture. The dimensions of the pad could be quite large as mentioned above. 2 methods to create the reverse image onto the gelatin pad from which the gel-lithograph is printed. The first is very similar to the blueprint method. The second method uses actinic inks, which are inks that react when put into contact with the gelatin because they contain ferric salts. The undeveloped blueprint or actinic ink is pressed onto the pad for 15 seconds. This causes the gelatin to harden in areas where it is in contact with the lines of ferric salts, while staying moist in all other areas. The intermediate blueprint or actinic ink original is pulled away and the gelatin plate is then rolled with printing ink. The oil-based ink will only adhere in areas where they gelatin has hardened. A non-sensitized sheet of paper or drafting cloth can then be placed on the pad in order to receive the image transfer. . The support must be well sized, otherwise it would absorb moisture from the gelatin pad, making it impossible to print more than a few copies. Up to 100 reproductions can be produced from a single pad. Afterwards, gelatin can be melted and reused. o Degradation: Prints are as permanent as the supports. o Storage: Can be safely stored with original plans. o Buffered / unbuffered / polyester: If document was printed on mechanical wood pulp paper, sized with alum and rosin, it is likely to be very acidic, brittle, and strongly discolored. Use buffered, paper folders and interleaving papers.


Hectographs (1870 – replaced by blueprints) Not photoreproductions or photomechanical reproductions, but similar in appearance to gel-lithographs and diazotypes o Line colors: any dye color, purple most common, image lines are feathery and not shop, may vary in density o Ground colors: o Positive / Negative: positive o Contrast: may be low contrast since aniline dyes fade rapidly especially if the support has discolored o Support: highly smooth and calendered paper o Magnified view: dyed fibers of the image lines can be easily using a loupe o Other: Could reproduce large drawings. A o Distinguish from others: o History and Manufacturing: Process is similar to the gel-lithograph, using a gelatin pad o Degradation: The aniline based image lines of hectographs are unstable under light. Exposure to any light, particularly ultraviolet, should be limited. Otherwise, as stable as the support on which they were produced. o Storage: o Buffered / unbuffered / polyester: If document was printed on mechanical wood pulp paper, sized with alum and rosin, it is likely to be very acidic, brittle, and discolored. Use unbuffered, paper folders. May use polyester sleeves to segregate from other types of prints and original drawings.

APPENDICES

General Storage Notes General environment – same as other paper-based storage Horizontal storage – in general, polyester enclosures are safest to prevent contact degradation and off-gassing. Another option is to use a 20 point medium paper stock folder such as map folders. Rolled storage – used when files are too large to be stored flat. Documents produced on brittle support should not be rolled. Roll items around a rigid tube of large diameter (at least 4”) so as not to induce stress. The core material should be acid-free cardboard [or covered with acid-free paper] Vertical storage – not recommended because the full weight of the paper, drafting cloth, or plastic film, rests on a very small section of the support, making it prone to tearing.

Handling and Exhibition Handling – support with a sheet of paper during handling, or enclose within a polyester sleeve. Cover with an opaque sheet of paper to prevent fading. Do not rest objects on top, except for loupes or weights for rolled drawings. Lighting – Many architectural drawings are very light-senstive. Light damage is cumulative. Filter fluorescent lights and windows to prevent ultraviolet light from reaching the image. Display a copy of the image instead of the original. Humidity and temperature – Keep RH relatively low, especially Vandyke prints and ferrogallic prints. Minimally, avoid repetitive fluctuations as the material expands and contracts with every change in RH and tempareatre. Mounting – If displaying originals, should be matted to reduce the risk of tearing. Use netrual pH mat board that has passed the PAT test.

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