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Tag: Molds

  • Playing With the Cure Time of Molds and Casts

    Playing With the Cure Time of Molds and Casts

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    Every mold making and casting material comes with its own specific range of cure time. This is nothing but the time that the material will take to get completely cured. It can range from just a few minutes to hours or even a few days. The mold or cast has to be left to air dry on its own and there is nothing much that the artist can do in the meanwhile.

    Similarly, the pot time or working time is the time on hand to work with the product after it is mixed until it starts to set. After this, the material will not work properly.

    For instance, alginate is renowned for its quick setting and curing time, whereas materials like latex rubber require days on end to cure before they are ready for use. Most silicones have a cure time between 18 to 24 hours.

    What to do?

    Artists use various measures to speed up or prolong the cure time. In fact, delayed-setting and quick curing options are available for alginates, plasters, silicone and other materials. Sometimes, fibers, fillers, talc or magnesium oxide (for plaster) are added to achieve the same effect.

    For certain materials like silicone, fast catalysts are also available. These can be added to the silicone rubber to significantly reduce the cure time, sometimes to even just an hour! Care is needed as adding too much catalyst may make the material start curing even before it can be applied.

    Alternatively, techniques like hot air dryer, dehumidifier or baking in an oven are used to hasten the cure time. In fact, plaster casts are often baked to reduce the curing time to 12 to 24 hours. However, too much of the hot air can also cause the mold or cast to crack or spall. Also, silicone does not react very well to heating from dryers or lamps; it may just break out in unsightly bubbles all over the mold or cast.

    Temperature variation

    It should be noted that the pot time and cure time is generally measured at normal room temperature. It will definitely vary depending on the atmospheric and climatic conditions prevailing at the time of working/curing. For instance, cooler temperatures tend to increase the pot time and cure time while warmer weather is sure to reduce both working time and cure time.

    This phenomenon can be easily used to vary the pot/cure time to suit your convenience when trying how to make molds. All you have to do is gently warm the material (both base and catalyst for two-part materials) before using them. This will speed up the chemical reaction and the mold or cast will take lesser time to cure. But keep in mind that the working time is also reduced and the material will start setting much more quickly. Do not overheat the materials either.

    Similarly, cure time can be easily increased by refrigerating the material (both base and catalyst again) prior to use of how to make molds. This will give more time for working with the material per se.

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    Source by Ed McCormick

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  • Dating Vintage Jewellery – The Back View

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    When I pick up a piece of vintage jewellery maybe a brooch, I almost immediately turn it over. Quite a few times the seller has commented “Its not gold or silver”.

    For me this is annoying as that is not what I am looking for.

    Gold and silver do not particularly interest me and more often than not I can distinguish fine jewellery at a glance before handling.

    So what am I looking for:

    First I am looking to make sure the brooch pin or back of the jewellery is intact and not broken/damaged.

    Then I am looking to see if there is a signature. With familiarity to various signed vintage costume jewellery pieces, I can now identify who the company or manufacturer is at first look for many pieces, without picking it up and looking at the back. So when you have a spare few minutes take a trip through the vintage jewellery websites and look at the photographs and companies.

    If there is no signature – the jewellery’s construction and the findings used can give valuable clues to dating. But more of that in a later article.

    Back to the signature. Look at the wording can give valuable clues to dates.

    First the name – Exquisite produced jewellery from 1914 until the late 1970s but their signature did not appear until after 1953 (confirmed information from an employer who made the jewellery’s molds) So any Exquisite jewellery with a signature dates to after 1953 to about 1979. Probably more accurately from 1956 but to be confirmed still.

    Look up the company to see when they were in production, will give a time span to work on. Most information is available now on the internet and you may be lucky to find when the jewellery was actually patented.

    The copy right symbol – the c in a circle mark means it was made after 1955. This was because Trifari won a lawsuit in that year, and everyone followed suit of copy right their designs rather than patenting them.

    How is the signature presented – in script, abbreviated, block letters, large capital letter for the first letter of the name then small letters. This can also help to date. Again there are many websites and Yahoo groups that can help. Exquisite, Miracle and Kenneth Lane are just a few that changed their signature and this can date them to when that type of signature was in use.

    Pat pending and design numbers are also clues. Pat pending dates to before 1955. Again many sites have lists of patents. Boucher and Sphinx are two companies that used numbers for their designs. With or without the name signature.

    So just looking at a signature on a plaque or cartouche can give you many opportunities for dating your vintage jewellery

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    Source by Susan C Weaver

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