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I'm trying to make sparks that fade out over time, and I'm pulling my hair out trying to get the nodes to work properly. It seems like the mix shader node is doing the exact opposite of what it's supposed to. This is my node setup:

enter image description here

Everything connected to the emission strength input is meant to control the spark's edge softness. I found it counterproductive to try to make a spark the edges of which you can see, so I set the brightness of the volume emission node to fade as it reaches the edges of the spark.

The mix shader node tree is where the problems are. Whenever I try to drag the factor slider on the mix shader node, nothing happens. I set the emission strength to be quite small, so that if it began to fade to transparent at all, I'd know. However, when I drag the slider, absolutely nothing happens until it hits 1. When it hits 1, the spark immediately goes from bright to invisible with no transition. I can get arbitrarily close to 1 (0.9999) and there's still no change. It only does anything when it hits 1.

This is exactly how the particle looks with a mix shader factor that's any less than 1:

enter image description here

This is what happens the second it hits 1:

enter image description here

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  • $\begingroup$ This question is similar to blender.stackexchange.com/questions/49128/… . Is it a repeat? $\endgroup$ – atomicbezierslinger Mar 21 '16 at 21:10
  • $\begingroup$ See answer below. Your factor for the mix shader is set to zero. That is fine for future flexibility ..... but at the moment you are getting one emission contribution and no transparency contribution. Mix factor of 1 or 0 are the extreme mixes of only one contribution. $\endgroup$ – atomicbezierslinger Mar 21 '16 at 21:16
  • $\begingroup$ @atomicbezierslinger It's not actually a repeat. It's a similar problem I was having, but I'm not actually sure if they're connected. I get the feeling the problems are both based on the particle info age output not giving an actual age as an output. I think I'm going to delete the previous question, and this one too, and create a new one. $\endgroup$ – Sanix25 Mar 21 '16 at 22:09
  • $\begingroup$ Did you understand my previous comment? Did you try the proposed solution below? Please try the solution and comment it as either .... difficulties are persisting ........ or the answer is successful. Your image of nodes is a little difficult to read ... for some reason it is blurry. Also you might consider changing the particle image to have a transparent background if you are trying to investigate transparency. $\endgroup$ – atomicbezierslinger Mar 22 '16 at 7:56
  • $\begingroup$ @atomicbezierslinger I know the mix shader factor is set to 0. That's not the issue I'm having. The issue I'm having is that when I manually adjust the factor, nothing happens. There is absolutely zero difference in brightness between a mix shader factor of 0, 0.5, and 0.999. But suddenly, the minute that the factor hits 1, it INSTANTLY goes from full brightness to completely invisible. I'm trying to get it to gradually lose brightness, but it won't. $\endgroup$ – Sanix25 Mar 22 '16 at 17:03
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Plug the Output of your Multiply Node into the Factor Input of your MixShader. You probably need to invert it before.

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If all particles have a circular fade one could consider billboards of the texture.

For the nodes of the original question. I suggest a constant multiplier value for emission such as 2.

If one adds a weighted sum of the (age/lifetime) plus the value of intended (1 - opaqueness), that sum can be used as the input to fac of the mix shader. It may be the poser of the question always wants a quadratic sphere texture style fade, with more opaqueness in the middle.

fac = x(age/lifetime) + y(1 - opacity)

The first time approaches 1 as age increases. The second term has a more opaque center of the quadratic style sphere. 0 < x <= 1 and 0 < y <= 1. If the sum is greater than 1, then zero clipping will occur, which may be acceptable. No effort has been made to preserve a bright center.

Image Below. Rendered image.

enter image description here

Problems encountered. If the nodes focus on transparency and generated coordinates there are some undesirable traits for some scenarios. If a spherical view is always desired than we can produce problems. In the image below see the hemisphere shape from a certain viewpoint. The two large spherical shapes use a different technique.

enter image description here

Alternative

Image Below. Rendered image.

enter image description here

A particle system with particles having the material below. An alternative Material Node collection.

enter image description here

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