You have used something like "gold gradient" It's especially unrealistic if it's used on several surfaces. You should notice that polished gold is like a mirror, only a colored one and generally so non-planar that the image is extremely distorted.If there's bright lights, they should be seen at least on some rounded edges.
Color of gold:
That depends on how much it's diluted with other metals and with what metals. I skip the differences between the common standard mixes.
I have used in several occasions as my base gold R=191 G=170 B=117. It's not especially gold looking alone and it's far more less saturated than many horrors I've seen.
Do not rely on the screenshot, use the numbers! There are far too many color conversions between my Illustrator and your screen.
It starts to resemble gold when it's used to colorize a grayscale image. Here it's placed with blending mode Color onto a white to black gradient:
As well you can have the grayscale image on top with blending mode = Luminosity and the gold base color in the background can have blending mode = Normal. This can be more convenient if you must tweak the grayscale image for the right appearance.
You may wonder why so often gold has more saturated colors. Something like orange can be seen in some used gold gradients, too. That's because the light isn't always white. If it comes as reflected from other gold surface, it's already colored and the next reflection increases that filtering. That can be coarsely simulated by multiplying two of my gold gradients which have different directions:
It's not the full truth due the non-linearity of our color sight, but be sure, that a single hue gold gradient isn't enough if your image has gold reflected from gold, for ex. you have a bunch of gold ingots. To keep it simple you must include more orange areas to the colorizing layer. You can pick the colors from a multiplied pair of single hue crossed gold gradients, just like the example. It's easiest in Photoshop.
Illustrator's 3D effects can create to some degree right looking shadings. They have wisely named the most glossy mode only to "Plastic Shading", so nobody should be disappointed, if he got no gold. But by careful light setting something acceptable can appear. Here's a rounded but otherwise quite random piece extruded and shown in 2 different angular positions:
As you see, it's really plastic, there's no shine. Illustrator hasn't good tools for tweaking the brightness and contrast. One trick is to add a dark grey low opacity overlay with blending mode "Color Dodge"
If you want glossy gold, you must insert the reflection by yourself. Many surfaces can have gradients, but we use also something else. At first the gradient:
A bended sheet has highlights at obvious places. There's a grayscale gradient giving its luminosity to a base gold version.
If you have dark shades in the reflection, the environment also must contain much dark Against white background this would seem dirty
You can use also blurred black and white shapes instead of gradients. It's not totally different, it's an alternative way to implement gradients.
In a complex environment you can reflect it. You should study how the environment reflects from chrome parts of a car. At least GIMP has chromium filter which takes a photo and make chrome-like distorted mirror images. With gold you need only the coloring as extra.
The gold ingot:
It has certain forms for easy mold casting. The surfaces are tilted and most edges are rounded. I sketched one in 3D:
This is a screenshot from entry level freeware CAD which definitely cannot make gold nor other material renderings. But the wireframe shape can be exported as 2D PDF. It can be opened in Illustrator:
I colored with the shape builder areas which need different colorings for gold. Grey areas can be solid greyshades or gradients. Brown areas must be gradients and they are most probable places of glossy highlichts.
If one thinks a moment, he sees that Illustrator's linear and polar gradients are too simple. One needs gradient meshes. They are complex and filling them succesfully to metallic glosses needs incredible amount of skill and patience.The job simply is beyond the possiblities of a beginner. But blurring is a way to cheat.
The wireframe of the ingot must be filled with the shape builder two times. One for the outline of the ingot and the other to get a base frame for blurs.
The latter needs some help lines. Actually it's like an ingot with no roundings:
One must decide the light. It fixes which greyshades are used as fill colors . The gradients need auxiliary white and dark lines at the edges. There are also seemingly uunecessary outline strokes added to the grey areas. They only make the shape bigger to compensate the thinning at the edges which is caused by the blurring.
My final base frame before blurring:
All is grouped and gaussian blur effect is applied:
We have the other filled wireframe which is the outline of the ingot. In the next image one copy of the outline is used as clipping mask for the blurred shape. Another copy is colored to base gold. It will give the color to the clipped shape:
The colored shape needs to be placed on the blurred shape with blending mode color. The result=a gold ingot:
It's not perfect, but well in the range of a beginner. You should notice that you do not need 3D program in any phase for this. The 3D wireframe was only a reference. All used shapes are easily drawn by hand.
Shape builder must be thoroughly studied before this.
One can want stamps or texts on his gold:
Illustrator's 3D extrusions can be useful. Here is actually extruded a hole ABC. The greyshades are set manually to fit. The inserted shape is in the right.
Rendering in a 3D program can create photorealistic results. They do not come out from simple software nor intentionally limited free versions of commercial programs. Here's an example: It's an old try-it-yourself version of Keyshot:
I have no way to force the bars to be considered as single continuous surfaces. If the surfaces are glossy, there are visible seams between the curved and planar faces. I bet competent Blender users would laugh for this. But one thing is shown plausibly: Gold reflected from gold has more full color, as told above.
Handcrafting in Photoshop:
Photoshop offers more flexibility than Illustrator. It's layer styles help to create glosses and shadows. An example:
It originally had the dark grey background, three layers for three visible surfaces and a coloring layer.
Surface layers were filled with different grayscale gradients to mimic environmental reflections. The fill areas were selected with the polygonal lasso tool, no vector paths were drawn
Each surface layer got layer style Bevel&Emboss to create the glossy and dark edges. Often the same effect is used to create also the surface wide gradients with extreme settings, but here only the edges were affected.
The coloring layer was filled with base gold and then faint orange were sprayed to areas which are dark in surface gradients
Bevel&Emboss edges fight at corners. One can insert layer masks to decide who wins who and where. I merged all and painted the corners with the cloning brush. It's a little grungy, but I see it usable.