Best way to get images off exposed E4 colour slide film?

I have several rolls of 35mm Ektachrome E4 rolls that have been exposed back in the 1970's and have been refrigerated/frozen for a good part of the time since then. I have checked out online some sites that claim to be able to process "as a negative" ... and then maybe put through some "color process" if the B&W results look promising. The prices quoted seem a bit expensive ... but it's a niche process, so that's understandable, I guess.

Can anyone suggest a site that they feel is reliable if I decide to go that route? And if anyone has any experience with a somewhat similar situation, please comment !! Thanks !

Many amateurs ran E4 as color neg using Kodak C22. I think if you used any B&W you would get a neg that could be printed amusingly on color paper at any photo lab. If the images have potential importance to you, you should do a snip test first. Me, id use Rodinal @ 1+50 30 minutes @ 70 deg with minimal agitation.

E-4 was quite a process -- 14 steps, as I recall. My high school photography class processed one roll for each student in an E-4 kit in 1975 -- took the whole afternoon, as I recall, but Ektachrome from a Reflex II was something to see!

B&W negative is probably the sensible way to process that film. Unlike color negative stock, it doesn't have an orange mask, though you might have to give it a short bath in Farmer's Reducer if it has a colloidal silver antihalation as some slide films had. My rule for old found film used to be HC-110, because it has such a strong anti-fog, but who knows if new HC-110 still has that. You could also try (after a clip test, or a single roll) something I ran across recently, processing at very low temperature (like 51 F!) with added benzotriazole, to clear out the fog of age. Again, a little Farmer's Reducer after processing can help here, too. Just be careful with that, as you're removing your shadow details along with the fog...

E4 is conceptually similar to E6 with some changes to chemistry mostly due to environmental/health reasons. Official E4 formulas can be found here: https://125px.com/docs/techpubs/kodak/cis111-E4_Forumulas.pdf
The complex 14-step process hinted at by Donald is probably K14 for Kodachrome, which is an entirely different animal.

Naturally, the hopes for getting decent images for film exposed this long ago should be limited. You could indeed develop as B&W and if the images come out sort of OK, bleach them back and color develop them for a color negative (without the orange mask obviously). Image quality will likely be severely compromised, but scanning and digital adjustments may yield something that resembles a presentable image - nobody will be able to tell for sure.

Alternatively you could try running the film through a modified E6 process with an additional pre-hardening step and reduced processing temperature (30C instead of 38C). Results, again, will be quite unpredictable and especially development time (esp. the first developer) will need to be experimentally established to give (somewhat) optimal results.

A final alternative is to just develop in a regular B&W developer and keep it at that, for a B&W negative. It's the most straightforward approach, but obviously, you'll have to do without the colors.

Depending on the importance of the images on the rolls it may be worthwhile to try it out, but don't get your hopes up too high. Getting some sort of image will be feasible; getting 'good' images (esp in color) is more or less out of the question.

E4 was very simple.. in good hands it was more color-accurate than E6 when that was first introduced. I processed a lot of E3 as well as E4 on reels in Nikor tanks, temp controlled in bathtube. I also processed several hundred rolls daily in Calumet nitrogen-burst tank line. It took a very bad lab to produce off-color E4, but most labs were in fact very bad back then.

Would be easy to formulate all the chemicals oneself, except for the TBAB in the color developer, which will be a really serious problem. It’s a very dangerous chemical, IIRC.

I guess the way to go is black and white negative.

Unless the TBAB can be dropped and a second exposure introduced... but this may require further modifications to the color developer.

E4 was easily processed as a negative using conventional Kodak C22 color negative chemistry (small kits are sometimes found on Bay).

I'd process the first 6" of film as a snip test.