Verb conjugation of "verdunkeln" in German

My boss offered it to me, so that a few more people at work will have a good level of English and now I really have to kick my own ass (I've started last year and it's not going very well).
Everything in your letter is perfect! Almost no errors and the writing style, very impressive! After this first year in England, you have also improved your vocabulary and the grammar skills.
That is a beautiful name you have got. It would be very helpful if you answered my mail before next week because I will have my final test on Wednesday. I will understand if you won't be able too.