Editing Shadow mask (section)

===Improvements, market acceptance===
By the 1960s the first RCA patents were ending, while at the same time a number of technical improvements were being introduced. A number of these were worked into the GE [[Porta-Color]] set of 1966, which was an enormous success. By 1968 almost every company had a competing design, and color television moved from an expensive option to mainstream devices.

Doming problems due to thermal expansion of the shadow mask were solved in several ways. Some companies used a thermostat to measure the temperature and adjust the scanning to match the expansion.<ref name=bright/> Bi-metallic shadow masks, where differential expansion rates offset the issue, became common in the late 1960s. [[Invar]] and similar low-expansion alloys were introduced in the 1980s<ref>[https://books.google.com/books?id=ZU1attzzKyMC&pg=PA35 "Taking the heat out of flat-screen television..."] {{Webarchive|url=https://web.archive.org/web/20171004085759/https://books.google.ca/books?id=ZU1attzzKyMC&pg=PA35 |date=4 October 2017 }}, ''New Scientist'', 3 October 1985, p. 35.</ref> These materials suffered from easy magnetization that can affect the colors, but this could be generally solved by including an automatic demagnetizing feature.<ref name=bright/> The last solution to be introduced was the "stretched mask", where the mask was welded to a frame, typically glass, at high temperatures. The frame was then welded to the inside of the tube. When the assembly cooled, the mask was under great tension, which no amount of heating from the guns would be able to remove.<ref>James Foley, [https://books.google.com/books?id=-4ngT05gmAQC&pg=PA160 "Computer graphics: principles and practice"] {{Webarchive|url=https://web.archive.org/web/20170202052745/https://books.google.ca/books?id=-4ngT05gmAQC&pg=PA160 |date=2 February 2017 }}, Addison-Wesley, 1996, p. 160.</ref><ref>{{Cite book|url=https://books.google.com/books?id=Frbtc4mssNQC&q=stretched+mask+tension+CRT&pg=PA24|title=Popular Science|date=1986|publisher=Bonnier Corporation|access-date=16 December 2020|archive-date=15 September 2022|archive-url=https://web.archive.org/web/20220915133929/https://books.google.com/books?id=Frbtc4mssNQC&q=stretched+mask+tension+CRT&pg=PA24|url-status=live}}</ref>

Improving brightness was another major line of work in the 1960s. The use of [[rare-earth]] phosphors produced brighter colors and allowed the strength of the electron beams to be reduced slightly. Better focusing systems, especially automatic systems that meant the set spent more time closer to perfect focus, allowed the dots to grow larger on the screen. The Porta-Color used both of these advances and re-arranged the guns to lie beside each other instead of in a triangle, allowing the dots to be extended vertically into slots that covered much more of the screen surface. This design, sometimes known as a "slot mask", became common in the 1970s.<ref name=bright>Len Buckwalter, [https://books.google.com/books?id=jCYDAAAAMBAJ&pg=PA142 "1970 Television: The Picture Is Brighter Than Ever"] {{Webarchive|url=https://web.archive.org/web/20171004085834/https://books.google.ca/books?id=jCYDAAAAMBAJ&pg=PA142 |date=4 October 2017 }}, "Popular Science", October 1969, p. 142–145, 224.</ref><ref>Jerry Whitaker, [https://books.google.com/books?id=8NUyB31nSvsC&pg=PA461 "DTV handbook"] {{Webarchive|url=https://web.archive.org/web/20171004085508/https://books.google.ca/books?id=8NUyB31nSvsC&pg=PA461 |date=4 October 2017 }}, McGraw-Hill, 2001, p. 461–462.</ref>

Another change that was widely introduced in the early 1970s was the use of a black material in the spaces around the inside of the phosphor pattern. This paint absorbed ambient light coming from the room, lowering the amount that was reflected back to the viewer. In order to make this work effectively, the phosphor dots were reduced in size, lowering their brightness. However, the improved contrast compared to ambient conditions allowed the faceplate to be made much more clear, allowing more light from the phosphor to reach the viewer and the actual brightness to increase.<ref name=bright/> Grey-tinted faceplates dimmed the image, but provided better contrast, because ambient light was attenuated before it reached the phosphors, and a second time as it returned to the viewer. Light from the phosphors was attenuated only once. This method changed over time, with <!--phosphor-dot surrounds in (?) -->TV tubes growing progressively more black over time.{{citation needed|date=November 2013}}

In manufacturing color CRTs, the shadow masks or aperture grilles were also used to expose [[photoresist]] on the faceplate to ultraviolet light sources, accurately positioned to simulate arriving electrons for one color at a time. This photoresist, when developed, permitted phosphor for only one color to be applied where required. The process was used a total of three times, once for each color. (The shadow mask or aperture grille had to be removable and accurately re-positionable for this process to succeed.)