At the other extreme, Mary, Queen of Scots (1542-1587), used invisible ink and ciphers to communicate with Catholic supporters. Her supporters wrote to her using two common substances: alum (hydrated potassium aluminium sulfate) or gall ink (tannic acid from parasitic wasps in oak trees galls). The alum letters would be developed by soaking the letter in water, and the gall ink would be developed by soaking the letter in iron sulfate solution.

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making and recording observations and evaluate the reliability of methods and suggest possible improvements; using appropriate techniques, apparatus, and materials during laboratory work, paying attention to health and safety; M iron sulfate IRRITANT, developed by 0.1 M sodium carbonate, 1% starch solution (e.g. corn starch or potato starch), or by 0.1 M iodine solution The paper can also be placed directly onto the hotplate on a low heat but greater care must be taken because it is more likely to burn this way if not supervised carefully. Going further: a b Selinger, Ben; Barrow, Russell (2017). Chemistry in the Marketplace. Clayton, Victoria: CSIRO Publishing. p.297. ISBN 9781486303328.Rigden, Denis (2001). SOE Syllabus: Lessons in Ungentlemanly Warfare, World War II. ISBN 9781903365182. Good results can be obtained from the heat method on milk, sodium hydrogen carbonate solution, vinegar (ethanoic acid), sugar solution and soapy water (sodium carbonate solution). Giovanni Battista della Porta is credited with the first recipe for a sympathetic ink, derived from alum and vinegar, as well as the first book on secret writing and invisible inks, Magia Naturalis (1558, 1589). [8] [4] :24 Since then, a wide variety of invisible inks have been used for all sorts of secretive purposes. A formula similar to oak gall ink was created by James Jay and used by George Washington and the Culper Spy Ring during the American Revolution and lemon juice was used by the 'Lemon Juice Spies' (Carl Muller and 4 other Germans, who all died for their efforts either by suicide or execution, along with John Hahn, an English baker) during World War I. [6] [4] In World War II, neutral or acidic solutions of phenolphthalein, a chemical compound extracted from pills for constipation, were used as invisible ink. [9] It is colorless but turns pink when exposed to alkali such as ammonia and bicarbonate soda. [9] General application and use [ edit ] reporting on findings from enquiries and observations, including oral and written explanations, displays or presentations of results and conclusions; Wheeler, Jo; Temple, Katy (2009). Renaissance secrets, recipes & formulas. London: Victoria and Albert Museum. p.98. ISBN 9781851775774.

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There are also toy invisible ink pens which have two tips—one tip for invisible ink writing, and another tip for developing the ink. Invisible ink is sometimes used to print parts of pictures or text in books for children to play with, always including a " decoder pen" which is used to show the invisible parts of texts or pictures, thus revealing answers to questions printed in regular ink or completing missing parts of pictures.Use their scientific knowledge to explain how changing the conditions the inks are under affects their visibility. presenting reasoned explanations, including explaining data in relation to predictions and hypotheses;

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The hotplate can be used on a low heat without the white tile, but it will have to be supervised as the paper could burn. It is safer to use a white tile on the hotplate to place the paper onto. It takes about 20–30 seconds on average on a low to medium heat setting for the message to appear. This means that a class practical could be carried out using a hotplate without congestion. There are some invisible ink types that can only be invisible when applied to certain types of surfaces, but are still visible on others.

Teacher and Technician Sheet

Potassium ferricyanide & phenolphthalein should not be used where there are naked flames (do not use Bunsen burners). Many of them work as pH indicators, so when in doubt, paint or spray a suspected message with a base (like sodium carbonate solution) or an acid (like lemon juice). Equipment: Miller, Bill (2001-06-13). "The Very Visible Battle Over Invisible Ink". Los Angeles Times. Archived from the original on 2010-07-06 . Retrieved 2010-05-02.

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Some inks glow faintly ( fluoresce) when under an ultraviolet lamp. This is a property of many substances, particularly organic substances and body fluids. Some UV-visible inks may be detected on a photocopy, due to the relatively strong ultraviolet component in light from the photocopier scanning head. The ink can be later made visible by different methods according to the type of invisible ink used. The ink may be revealed by heat or by application of an appropriate chemical, or it may be made visible by viewing under ultraviolet light. Inks which are developed by a chemical reaction may depend on an acid-base reaction (like litmus paper), reactions similar to the blueprint process, or any of hundreds of others. Developer fluids may be applied using a spray bottle, but some developers are in the form of vapor, e.g. ammonia fumes used to develop phenolphthalein ink. Using my scientific knowledge to explain how changing the conditions the inks are under affects their visibility. The discussion can be approached using the Special Operatives Executive (SOE) properties for ‘ideal’ invisible ink as the evaluation criteria.Telltale signs of invisible ink, such as pen scratches from a sharp pen, roughness, or changed reflectivity of the paper (either more dull or more shiny, usually from using undiluted ink), can be obvious to a careful observer who simply makes use of strong light, a magnifying glass and their nose. Also, key words in the visible letter, such as "heat" or any other odd code name, in an out of place context may alert a censor to the presence of invisible ink. Invisible ink is not effective with glossy or very smooth paper types, since the sizing of these papers prevents ink from being absorbed deep into the paper and it is easily visible, especially if the paper is examined under glancing light. There are, however, commercially available inks for non-porous surfaces that are only visible under ultraviolet light and are otherwise virtually invisible on such surfaces.