Next This revision bite looks more closely at the first purpose of writing which is examined in Standard Grade English - to convey information.
History[ edit ] The effect of light in darkening a prepared paper was discovered by Thomas Wedgwood in After the early days of photography, papers have been manufactured on a large scale with improved consistency and greater light sensitivity.
Types of photographic papers[ edit ] Photographic papers fall into one of three sub-categories: Papers used for negative-positive processes.
This includes all current black-and-white papers and chromogenic colour papers.
Papers used for positive-positive processes in which the "film" is the same as the final image e. Papers used for positive-positive film-to-paper processes where a positive image is enlarged and copied onto a photographic paper, for example the Ilfochrome process.
Structure[ edit ] All photographic papers consist of a light-sensitive emulsionconsisting of silver halide salts suspended in a colloidal material - usually gelatin - coated onto a paper, resin coated paper or polyester support.
Black-and-white papers[ edit ] Modern black-and-white papers are coated on a small range of bases; baryta -coated paper, resin-coated paper or polyester.
In the past, linen has been used as a base material.
This is called a supercoating. Papers without a supercoating are suitable for use with the bromoil process. These papers require careful processing and handling, especially when wet.
However, they are easier to tonehand-colour and retouch than resin-coated equivalents. Since no chemicals or water are absorbed into the paper base, the time needed for processing, washing and drying durations are significantly reduced in comparison to fiber-based papers.
Resin paper prints can be finished and dried within twenty to thirty minutes. Resin-coated papers have improved dimensional stability, and do not curl upon drying. However, the substance used to coat photographic papers is usually not pure barium sulfatebut a mixture of barium and strontium sulfates.
The ratio of strontium to barium differs among commercial photographic papers, so chemical analysis can be used to identify the maker of the paper used to make a print and sometimes when the paper was made.
The brightening occurs because barium sulfate is in the form of a fine precipitate that scatters light back through the silver image layer. In the early days of photography, before baryta layers were used, impurities from the paper fibers could gradually diffuse into the silver layer and cause an uneven loss of sensitivity before development or mottle unevenly discoluor the silver image after development.
The photographic emulsion used for colour photographic materials consists of three colour emulsion layers cyanyellowand magenta along with other supporting layers.
The colour layers are sensitised to their corresponding colours. Although it is commonly believed that the layers in negative papers are shielded against the intrusion of light of a different wavelength than the actual layer by colour filters which dissolve during processing, this is not so.
The colour layers in negative papers are actually produced to have speeds which increase from cyan red sensitive to magenta green sensitive to yellow blue sensitiveand thus when filtered during printing, the blue light is "normalized" so that there is no crosstalk.
After adding enough yellow filtration to make a neutral, the blue sensitivity of the slow cyan layer is "lost".
This is the reverse of the usual layer order in colour films. Type R prints, which are no longer made, were positive—positive chromogenic prints.
Black-and-white papers typically use relatively insensitive emulsions composed of silver bromidesilver chloride or a combination of both.
The silver halide used affects the paper's sensitivity and the image tone of the resulting print. Chloride emulsions are also used for printing-out papers, or POP, which require no further development after exposure.All Round Education Academy offers world-class service of a private tutor in Hong Kong, helping students to become independent learners in their academic performance.
Sixth Grade (Grade 6) English as a Second Language ESL questions for your custom printable tests and worksheets. In a hurry? Browse our pre-made printable worksheets library with a variety of activities and quizzes for all K levels.
I have grade 6 new syllabus science and maths papers let me know how to upload them to this blog. Thanks Hemantha. Reply Delete. For Maths tests children require: A pen and pencil. A ruler displaying both cm and mm.
An "angle measurer" (protractor). A mirror.
Tracing paper. Where a calculator is . Private Bag X Nelspruit South Africa: Disclaimer. TOLL-FREE: Government Boulevard Riverside park Building 5 Nelspruit Conquesta Past Papers offers past exam / test papers as a teaching aid or learning aid for use at home and/or in the classroom.
These scripts can be used as an extra mural activity.